> In fact, I can't name a single service I've ever used (ever!) that lets me change my username.
Facebook? Twitter? Instagram? Any of the phone-number-based social apps (which have a poorer UX because of it, but still all allow changing usernames seeing as phone numbers change)? Also I believe Skype does allow changing usernames.
Hotmail Gmail
Seriously why can’t people change their email and keep the mailbox. It’s not uncommon to pick a cute or funny email when you are a teen and want To change when you’ve all grown up
you mention Facebook but isn't it just your display name that you can change? your username (the page listed under "username" if you tap your face in the Messenger app, or on the desktop web app, the page you're at if you click your icon with your name next to the search bar) doesn't change, does it? (maybe I'm wrong and it does.)
Facebook lets you configure both your Name (display name) and Username (the URL slug for your profile) separately. You can even edit your Username right from within Messenger if you want.
Facebook? Twitter? Instagram? Any of the phone-number-based social apps (which have a poorer UX because of it, but still all allow changing usernames seeing as phone numbers change)? Also I believe Skype does allow changing usernames.