If anything, it discourages changing usernames for no reason (as in you changing your name for no reason, there certainly is a reason behind the decision to limit name changes)
What would happen if you do it by accident or a friend of yours just messed around and used up all 5 name changes? (I know it is a very low probability, however the chance isn't zero)
I believe I changed my name once, probably days after making an account, name changing is definitely a necessary feature but I don't see why you'd need it more than 5 times, I've seen quite a few people use it to change their name to someone else's so it is probably best to keep a limit. 5 seems fine enough.
I have changed my name 3 times. 1 to change my name from PontiacLover to just Pontiac and then the other two times was for April Fool's when I switched names with my alt account.
I've always had the same username, however I can see a situation where a new user comes in, creates an account, but inadvertently spells the name wrong, notices it at a later date and wants to change slightly.
I think 3 is more than enough to cover this eventuality.
Five seems like a lot, to be honest.
1) Any name that anyone has ever had is now off limits to anyone but that user.
2) The user's url is changed when they change names, but redirects are handled automatically
3) AI reviews names for vulgarity. Unfortunately there was a lot.
I think 3 is more than enough to cover this eventuality.