I think for many what didn't help was this:
And gameplay wise they were all four pretty much identical as well. The original four games did not only look distinctly different from one another, but they also played very distinct from one another.
I don't know what point you're trying to make showing how the 4 NSMB look different from each other.
This look for the Mushroom Kingdom was essentially cemented with the SNES games.
Someone really liked those pill-shaped mountains.
The SMB games have always had a linear progression in how they developed.
SMB2 was very similar to SMB1 with some small new mechanics like wind and different graphics.
SMB3 was the biggest change the series had. Screens could scroll left and right
or up and and down instead of just 1 direction, so you could backtrack. Lots of new powerups including flight. World themes like desert, ice, etc. World maps. The p meter. Can now hold items like shells.
SMW started out using SMB3 as a base, but they tweaked the air physics to make the game easier because they wanted it to be more friendly. Regressed back to SMB1 and 2 themes. Added spin jump. Made the P meter invisible. Levels can now be 2 screens tall and n screens wide or n screens tall and 2 screens wide. More open map style. Yoshi.
NSMB added wall jumping and ground pounding. Physics are a cross between SMB3 and SMW. Screens no longer have restrictions on scrolling and can be as tall and wide as they want. Added lots of new mechanics they couldn't do be fore like warping terrain and rotating stuff. Introduced Star Coins. No flying powerup but there were level specific flight moments.
NSMBWii added multiplayer for the first time. Introduced the mid-air twirl. Ice Mario and Penguin are great additions.
NSMB2: Heavy focus on collecting coins. Was made by young blood getting their feet wet.
NSMBU: Brought back SMW style map. 5 players. Challenge mode.
The thing is, Mario essentially fully realized its identity with the 3rd game, and everything since has been building on that. Games have gotten to the point where it's easier to make your game look like the concept art and changes from game to game are more subtle than they were when generational leaps in power had a bigger impact on how games looked.
It's disingenuous to basically point at this:
And go "Yeah, they are different, but not as noticeably different as the older games!" That's a substatial visual upgrade.
And at this point the gameplay is essentially perfect, so innovation is more on the level design and mechanics side, which the NSMB games deliver on in spades.