Why people hate gambit so much? I mean one thing is that fans do it, but that writers actively try to sabotaje him is too far
There's no clear answer for it, but it usually comes across as them feeling like Gambit came after their time, and a weird jealousy that he's gotten spotlight over their favorite characters in the past.
There's this strange perception that Gambit's popularity is undeserved because of he got to be a in the X-Men cartoon instead of characters that had been around longer. Also, that he's only popular because of the cartoon, even though he was put into the cartoon because he was blowing up in the comics at the time and was part of the best selling comic in history to this day.
The ways they attack Gambit are pretty hypocritical, too.
His accent is no worse than, say, Nightcrawler, Colossus, Rogue, or Banshee unless the writer is going out of their way to make it cartoonish. Somewhat cartoonish accents have been a part of X-Men since the 70s, and they've been toned down over the years, including Gambit's. Gambit's accent is as X-Men as time travel, alternate realities, and psychic projection body armor.
Then there is the accusation of him being a creeper and shallow womanizer, despite the only character he actually pursued being a near invincible superwoman that could kill him in seconds if he touched her, which he knew. Wolverine's weird behavior towards Jean Grey was fine, though. Also, Cyclops is no problem even though he abandoned his family when his previously dead girlfriend showed up suddenly, then he ended up cheating on that girlfriend later, anyway.
People also try to say that there are no good Gambit stories, which is true if you're only familiar with the main X-Men books post-1995 or so, but really, it just means they haven't read any actual Gambit stories. The best Gambit stuff isn't in big X-Men events. It's his solo stories or smaller scale X-Men issues in between the big events.
And Gambit doesn't have a story like God Loves Man Kills or Watchmen or The Killing Joke, but none if any of the solo X-Men stories are on that level. Very few superhero comics are. He's consistently fun in a way that evokes Danny Ocean, James Bond, Han Solo, or Indiana Jones at different times, so the idea that he can't carry a movie is ridiculous. He has plenty of solid character examination, too, usually rooted in his weird messed up upbringing vs. his instincts to do good and redeem himself, and the best Gambit stories (as Fabian Nicieza, the guy that is responsible for most of Gambit's core characterization and also created Deadpool, said) are ones that put Gambit in situations where there is no clear right answer for him, and he comes out even more compromised. There's some really good stuff with this in his 1999 solo series, which reading at least the first 10 issues of should be considered a prerequisite for knowing what the fuck you're talking about when it comes to Gambit.
There are plenty of valid reasons to dislike Gambit as a character, but saying he's an inherently terrible character with no good stories that couldn't work as a movie lead is just a mountain of bullshit.
But a lot of people want to see his movie and his character fail, again, often due to this weird jealousy and hypocrisy thing, even though Gambit's success wouldn't do a damn thing to hurt their favorite's opportunities. So they will say and do whatever reductive bullshit they can to draw attention to and exaggerate the character's perceived irredeemable flaws and dated qualities that couldn't easily be changed by a new writer like they have for many other characters. Batman is still the same character as he was in the Adam West show, isn't he? And he didn't get his best, character-defining stories until around 40 years after his creation, right?
At the end of the day, if a Gambit movie gets made, it's going to come down to the trailers and the Rotten Tomatoes score whether or not people see it. And if a Gambit movie succeeds, that's not going to hurt anything at all. The absolute worst thing would be that Tatum surprises everyone and gives us a kickass Gambit and is then immediately recast in an MCU X-Men reboot, but even that is fine. A movie can stand on its own. Not everything needs to be part of a series or cinematic universe.
tl;dr - It not Gambit, it you.