Like, I’m probably answering myself here but I think it is pointed out by gatekeepers who can’t stand the idea of community growth and everything should adhere to some other unfound arbitrary way to keep things ‘pure’ in a community.
When they forget that they too, started out as new and that they too probably have had other people sneer at them for simply being new. So now they go around and pretend this is some kind of ultimate shut-down insult to people who’re just trying to contribute to the fediverse by devaluing it by saying “OH U JUST SOME DAY OLD ACCOUNT, NOBODY SHOULD MIND THEM!”.
It’s like the false positive/negative game. If you are an actual person, then waiting a week or two for your account to mature in age is but a mere inconvenience to you. In comparison, keeping all the fresh spam/bot accounts off the platform is much more difficult. So the general consensus is to slightly inconvenience new users in the beginning in favor of having a better community in the longterm.