About Big Mac's romance, one thing to keep in mind is that for a side character like him, the only way his personal relationships would be developed is for the sake of a story. That is to say, he only got a girlfriend at all because they decided to make "Hard to Say Anything". They didn't make that episode to develop his love life.
Let's break down that episode. The story is that Big Mac falls in love with a mare from another town that neither he nor the CMC know well. The CMC help him try to win her over, without knowing much about her, and a love rival gets between them. The key part is that they don't have a personal connection to the mare or anyone the mare knows which knocks out Cheerilee and Marble. Now as to why they chose Sugar Belle, (1) it allowed them to showcase Starlight's Village in a one-part story, (2) she's established as a baker, providing a reason for them to connect, (3) Sugar Belle's VA (Rebecca Shoichet) is already a regular (though this is true for Cheerilee and Marble too), and (4) with Belle in her name, they could make Beauty and the Beast jokes.
With Marble, I get the feeling they did intend for her and Big Mac to be a thing, but then they realized pushing how Applejack and Pinkie may be related would mean Marble and Big Mac may be related. With Cheerilee, despite the hinting at the end, the entire point of "Hearts and Hooves Day" is that the CMC were going too far in trying to get them together. Especially for kids, it would be confusing to say that then go ahead and hook them up regardless.
Art dump.
1.「radical accelaration」/「マリア・Clars」のイラスト [pixiv] - Rainbow
2.Princess Luna's dream by RaikohIllust on DeviantArt
3.The Grand Galloping Gala by CCKittyCreative on DeviantArt - Mane Six
4.Look who caught the cat! by LooknamTCN on DeviantArt - EQG Rarity and Applejack in Miraculous cosplay
5.My Little Fluttershy by Jeremywithlove on DeviantArt - Human, younger
1.Magic Sparkle by Darksly-z on DeviantArt - Twilight
2.Fluttershy redo by ShroomBanan on Newgrounds
3.EQG Twilight and Sonata at cafe by xp_r6
4.Princess dress glimmy by Marenlicious on DeviantArt
5.T35 by Hierozaki on DeviantArt
1.School Girl Aria by TheBrokenCOG on DeviantArt - There's also a similar image for Sonata, but that has a panty shot.
2.KDA Scootaloo by yourfavoritelove on DeviantArt
3.Her Biggest Fan by WanderingPegasus on DeviantArt - Rainbow X Pinkie
4.Rarity by Feathers-Ruffled on Newgrounds - Anthro
5.Rarity by poneko-chan
1.Oleander posing by ginsengandhoney
2.Oleander with open book by ginsengandhoney
3.In her shadows by CastASpellLiana on DeviantArt - Sunset and Celestia
4.Golden Oak Library by Nemo2D on DeviantArt - Twilight
5.Burger eating Twilight and Sunset by tjpones
1.Commission by Holivi on DeviantArt - Anthro Cadance making graffiti
2.boooring by mirroredsea on DeviantArt - Lyra
3.Hi! by mirroredsea on DeviantArt - Twilight and Rainbow
4.coffee by mirroredsea on DeviantArt - Pinkie
5.Concern by yuyusunshine on DeviantArt - Rarity X Spike
1.Poniess 2018 by Mickeymonster on DeviantArt - Mane Six
2.Maud about to get wriggity wrecked by tjpones
3.horse by WanderingPegasus on DeviantArt - Fluttershy
4.Fluttershy dressed as Seabreeze the breezie by tsitra360
5.Pinkie pie in the garland by Jun1313 on DeviantArt
1.Gallus by Starlord-wannabe on DeviantArt
2.Pinkie Japanese New Year by bbtasu
3.Happy new year, Twilight by Margony on DeviantArt
4.-New Year!- by Heddopen on DeviantArt - Rainbow
5.Twilight New Year by colorfulcolor233
1.Sunset animated desktop wallpaper by howxu
2.Princess Cadance by little-pancakes on DeviantArt
3.Autumn Blaze - White by SambaNeko on DeviantArt
4.Fluffponk by Madacon on DeviantArt - Pinkie
5.Without exceeding by PyroPk on DeviantArt - Celestia
Fan-focused 2018 recap
Animation using song from The Lion King musical, covering an AU where Celestia turns evil instead of Luna.
Starlight traps Discord in a bunch of mobile games.
Let's break down that episode. The story is that Big Mac falls in love with a mare from another town that neither he nor the CMC know well. The CMC help him try to win her over, without knowing much about her, and a love rival gets between them. The key part is that they don't have a personal connection to the mare or anyone the mare knows which knocks out Cheerilee and Marble. Now as to why they chose Sugar Belle, (1) it allowed them to showcase Starlight's Village in a one-part story, (2) she's established as a baker, providing a reason for them to connect, (3) Sugar Belle's VA (Rebecca Shoichet) is already a regular (though this is true for Cheerilee and Marble too), and (4) with Belle in her name, they could make Beauty and the Beast jokes.
With Marble, I get the feeling they did intend for her and Big Mac to be a thing, but then they realized pushing how Applejack and Pinkie may be related would mean Marble and Big Mac may be related. With Cheerilee, despite the hinting at the end, the entire point of "Hearts and Hooves Day" is that the CMC were going too far in trying to get them together. Especially for kids, it would be confusing to say that then go ahead and hook them up regardless.
Art dump.
1.「radical accelaration」/「マリア・Clars」のイラスト [pixiv] - Rainbow
2.Princess Luna's dream by RaikohIllust on DeviantArt
3.The Grand Galloping Gala by CCKittyCreative on DeviantArt - Mane Six
4.Look who caught the cat! by LooknamTCN on DeviantArt - EQG Rarity and Applejack in Miraculous cosplay
5.My Little Fluttershy by Jeremywithlove on DeviantArt - Human, younger
1.Magic Sparkle by Darksly-z on DeviantArt - Twilight
2.Fluttershy redo by ShroomBanan on Newgrounds
3.EQG Twilight and Sonata at cafe by xp_r6
4.Princess dress glimmy by Marenlicious on DeviantArt
5.T35 by Hierozaki on DeviantArt
1.School Girl Aria by TheBrokenCOG on DeviantArt - There's also a similar image for Sonata, but that has a panty shot.
2.KDA Scootaloo by yourfavoritelove on DeviantArt
3.Her Biggest Fan by WanderingPegasus on DeviantArt - Rainbow X Pinkie
4.Rarity by Feathers-Ruffled on Newgrounds - Anthro
5.Rarity by poneko-chan
1.Oleander posing by ginsengandhoney
2.Oleander with open book by ginsengandhoney
3.In her shadows by CastASpellLiana on DeviantArt - Sunset and Celestia
4.Golden Oak Library by Nemo2D on DeviantArt - Twilight
5.Burger eating Twilight and Sunset by tjpones
1.Commission by Holivi on DeviantArt - Anthro Cadance making graffiti
2.boooring by mirroredsea on DeviantArt - Lyra
3.Hi! by mirroredsea on DeviantArt - Twilight and Rainbow
4.coffee by mirroredsea on DeviantArt - Pinkie
5.Concern by yuyusunshine on DeviantArt - Rarity X Spike
1.Poniess 2018 by Mickeymonster on DeviantArt - Mane Six
2.Maud about to get wriggity wrecked by tjpones
3.horse by WanderingPegasus on DeviantArt - Fluttershy
4.Fluttershy dressed as Seabreeze the breezie by tsitra360
5.Pinkie pie in the garland by Jun1313 on DeviantArt
1.Gallus by Starlord-wannabe on DeviantArt
2.Pinkie Japanese New Year by bbtasu
3.Happy new year, Twilight by Margony on DeviantArt
4.-New Year!- by Heddopen on DeviantArt - Rainbow
5.Twilight New Year by colorfulcolor233
1.Sunset animated desktop wallpaper by howxu
2.Princess Cadance by little-pancakes on DeviantArt
3.Autumn Blaze - White by SambaNeko on DeviantArt
4.Fluffponk by Madacon on DeviantArt - Pinkie
5.Without exceeding by PyroPk on DeviantArt - Celestia
Fan-focused 2018 recap
Animation using song from The Lion King musical, covering an AU where Celestia turns evil instead of Luna.
Starlight traps Discord in a bunch of mobile games.