The issue is that there isn’t really anything more to choosing an instance than just picking one though, and we don’t want to funnel every new user to a single instance lest this end up becoming just reddit with extra steps. Or the reccomended instance gets flooded with more traffic than it can handle.
At most, a new user may want to look at what instances have defederated from the one they want to sign up on, but that’s a concept that isn’t going to make sense to someone who is already having trouble understanding “sign up somewhere, interact with everywhere” setup.
Numerous guides to all of this have been created. Rather than tilting at windmills (you will never stop people from being rude online, best to just accept it) your effort would be better spent being the friendly guiding hand. That’s far more effective than trying to call out people who probably don’t care whether we’re attracting more users or not.