Now this I totally agree with. It's 100% not done out of malice. I'm very sure that most of the players that I've dealt with over the years wouldn't dream of doing this out of spite. I think largely what happens is that players often get a concept in their head that they want to play.
The DM announces that a new campaign is going to start up and the players start spitballing different concepts. And, often, they come up with a concept before session 0 has hit the ground. So, they're already coming in with 3/4 of a character already on the go. I know I've tried multiple times to insist that character generation be done as a group activity, only to have players come with fully formed characters pretty much every single time.
So, as a player, putting me on the spot and saying, "You must come as a blank slate, and do all your character creation right now," is a great way for me to end up with a character I'm not really interested in playing, and that probably won't be all that interesting for others to play alongside, either. If you aren't going to give me much time to think about it, how about you just hand me a pre-generated character, and be done with it?
If you're playing in Forgotten Realms, you have literally tens of thousands of pages of material to draw from.
Corollary: if you are playing in the Forgotten Realms, you have to go through literally thousands of pages before you can really grasp what's available.