Yes, to a degree I agree with what you are saying. However, I don't feel like the characters should be so "othered" that they feel completely disconnected from the setting in play. That seems to occur quite a bit, or at least I have a perception that it does, which leads the DM to shoehorn a justification for a pacifist Pixy Paladin (say that three times fast

) being in the world in the first place because that's what Bob brought to the table from his roster of characters he's got waiting to see play.
Perhaps. But this brings up another aspect.
You mention the players having a stable of characters, or at least character concepts. Something I have noticed is...a lot, and I mean a LOT, of GMs don't really want their players being very creative or offbeat with their characters. They want extremely "normal" people. Preferably human or (with major dispensation) the Tolkien options. Preferably "core four" classes or, with slight reluctance, the nearby classes (e.g. Druid, Ranger, Paladin, Barbarian, Bard), and preferably not the "weird" ones (Artificer, Monk, and Warlock in particular). These GMs may even ban any other races or options. Other elements (e.g. personality) allow quite a bit of freedom, but in terms of what the character is and what they do, a lot of GMs are pretty sharply limiting what players can choose and don't have much (if any) patience for players who have even somewhat different interests/preferences.
So, if these are players whom you know have played in many other games, what would this effect have on their preferences? They've been asked to play the same mostly-human characters over and over for years. From
your perspective, it might look like they're trying to be disruptive. From theirs, they're finally getting allowed to pull out one of the concepts they've had to hold in the bank for years because they so rarely get the chance to.
Obviously this won't be true of every group or every player. But it's just another example of why this kind of behavior might happen. When so, so, so many GMs out there are ultra-traditionalist, the
player might feel a strong motivation to break the mold. Conversely, the GM might say, "why is it MY game has to be the game where folks do that?" And there is no good answer. Because it isn't your fault that you have a "please fit in seamlessly with the world around you" preference, but when
almost every GM has that preference, it's going to chafe for a player base with more diverse tastes.