I'm sure it's a combination of different factors. I think there are some players who have been building a concept and want to use it in whatever next campaign they can get into. I think there are also players that have a theme (either mechanical or fluff wise) that they build around. I think the crux of the issue is that the creation and character choice is happening independently of the setting and campaign oftentimes. This isn't just my group, I see group compositions all the time on reddit that are very much what I'm describing.
Let me clarify that my use of the "crown" wasn't to be disparaging, I'm not in the business of telling people they are having badwrongfun, rather it's a feeling and something I see around the table and throughout the community; a certain level of one-upsmanship you might say.
Like I've said previously, the group as a whole should work together to make a great game, but I feel that the general sentiment in the community is that if a DM sets restrictions they are "selfish" and "aren't cooperative" when frankly, they are often the ones putting the most into any one game. I'm not saying DMs should be dictatorial, but players should cut them some slack and maybe they can DM a game with less restrictions in mind when the campaign is over? But many players don't want to do that for a myriad of extremely valid reasons (no problem!) but then they lose a little bit of the agency that is ceded to the DM by the very nature of that role.