system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why does a big social network like Twitter let me change my username, but virtually no other websites don't? 

I my have used hyperbole, but right now I'm very upset that there is no way to change my Snapchat username. (I spelled hungry as "hugry" and me being Asian doesn't help the situation) 

But I've always wondered why Twitter still lets me change my username. I thought they would stop letting people after it grew bigger--but nope. I can be JBlove95 one day and OnEdIrEcTiOn4LifE another as long as no one else uses them. 

Is there a special reason? 

*edit: ELI5 how do I change the title ;_;
gpt
Probably how the database that stores all the account information is set up.  There needs to be a unique field for each account - either an account number or a username that nobody else can have. Allowing the user to change names means that all the other inter-linked things with that name, all the assosciations with other databases and so on, may be lost - or, the computer system will need to go through each of these and update each one, which is a pain in the ass and uses computational power that could be used elsewhere, which increases the risk of downtime just to keep a few people happy who change their names for stupid reasons many times a week.

Imagine if a bus company randomly decided that the number 44 was now the number 55.  It would have to go around every bus stop and update the entire timetable, then update it's online timetables, then it'd have to deal with all the people that get pamphlets with the timetable on who have missed the 44 because it's now the 55.  It's easier just to not do it.