It doesn't matter if people like it. People liked Marvel 2 when it took over. Same for the Street Fighter games. It's that those game's time was over and it was time for something new. Consider the following:
Why is the Smash community the ONLY community who plays an outdated version of the series?
How is it OK when everyone else who cares about the series is playing a newer version but the tournament players are playing the older one?
I see this argument somewhat often, but this comparison to traditional fighters just doesn't work here. When you look at why things are as they are, Smash Bros and traditional fighters are almost total opposites in this regard. People don't move on to a new game just because it's new, and they won't play a game they don't like.
Other fighting games prioritize having solid mechanics because that's their main draw, it's what keeps players coming back for more, and for the most part it's all they really have. Smash Bros isn't just a fighting game, it's a celebration of Nintendo and is first and foremost meant to be a casual experience, its main appeal is more a sum of its parts compared to traditional fighters. High level play and the communities that have spawned around other games have generally been embraced and supported when it comes to traditional fighters, historically that hasn't been the case with Smash Bros. Even at the design level things like combos (which were a glitch in SF originally) became appropriated as a legitimate mechanic in future installments, while wave dashing is removed because it doesn't fit the direction Sakurai wants to take the series.
To elaborate further, the last point and the first one are related. Installments in the SF series are different from each other and people don't always like the mechanical changes that get made, but the reason those players move on is because new games still remain true to the core of what makes SF what it is. For the few things that change, there are also a lot of things that largely stay the same. A lot of people may not have been satisfied with Brawl as a competitive game, but it still does what it set out to and remains true to the core of Smash. Melee sort of just happened and picked up a strong competitive following along the way, but the nuances of the mechanics that made it so appealing as a competitive game (at least as far as Sakurai is concerned) are not a part of Smash's core.
Inversely solid mechanics are what traditional fighters are all about, and it's natural that the players who are the most in tune with those mechanics are valued. Those players can transition from game to game easier because there is no massive shift like a Melee -> Brawl type transition. If SF4 was released with nerfed stun on all grounded attacks that left you punishable on hit, jumping attacks that did massive stun, no reliable anti airs, and a broken block mechanic that didn't let you alternate between high and low in a block string, nobody would play it. In addition to being shallow and a massive downgrade compared to previous SF titles, the game would cease to play anything like an SF game.
I'm not taking shots at Brawl here or trying to call it a shallow game (it has its own merits), my point is that Smash and these other games are focused on totally different things. I've said this before, but people stuck with SF4 because it has merit and it's worthy as a Street Fighter title, not because it has Street Fighter in the title. Smash isn't like that, as while the sequels do stay true to themselves as Smash Bros games, they do not do the same as competitive fighters. After Melee it was Sakurai's call on what to do next, and he chose to stick with his original intent by taking the game in the opposite direction.
Smash Bros and other fighters are not in the same boat at all. Telling Melee players to move on is like telling Marvel players to move on to SF because there will never be an MvC4. The games are just too different. If people choose not to move on it's not because they can't adapt or get with the times, it's because they feel they have nothing to move on to.
Also, a few examples:
Street Fighter X Tekken - This game wasn't going to replace SF4 but it did have a lot of hype behind it.The game died out shortly after release, but it wasn't just because of the whole disc locked content issue. It earned the nickname Street Fighter X Timeout for a reason.
King of Fighters XII - Not a very good game, at all. KoF XIII does a complete 180 and now it's bigger than ever with 2 strong Evo showings attached to it.
BlazBlue - Not necessarily bad, but initially Guilty Gear players were looking to it as a spiritual successor. It didn't deliver on that so a lot of them went back to GG, and now BB has its own community.