@Gargron At first I thought it was lame but when I read their argumentation it makes sense.
It would be easier for people and their irl friends or acquaintances to remember the username if it doesn't have error-prone numbers attached to it.

Personally I think it's good to be accommodating to new users rather than overly loyal to older ones out of fear of backlash. At the end of the day, it's a minor inconvenience for us, but a better system for newcomers.