I try my best to never have a number in my name, I've had symbols though when I was a scenester and symbols were KEWL. But besides that I never put a number in my user. I have a few "standard" names that usually aren't taken on sites, and this is one of them, if they're taken I just assume I made an account years ago. XD
I am very uncreative and it takes me ages to think of a username so if I find out my username has already been taken I'll just tack on some extra numbers because it's easier than me sitting there trying to think of something new! I will try to user underscores or dashes first, if I can, because I do prefer the look without the numbers but it's not the end of the world for me if I do need to add numbers. I wish I could've had just Lumi but when I tried it told me the username was already taken so I added dashes, however if I had to I likely would've added numbers as well.
Generally for numbers I just pick my favourite ones but I think it's sweet when people use numbers that represent a family or friends birthday.
Sometimes you just want to stick with the same username, so you don’t have to remember a different one lol
Short term memory problems
I know in Nookazon and twitter Bluebellie was taken, so I just added a 1 on there. I only use those sites for animal crossing and don’t want to have to remember another username. Kind of wanted everything the same.
As some others have said, for me it's because I'm not creative so I just add on the numbers if need be. I have been lucky enough to avoid username with numbers most places but there are a few places where I do use numbers.
Started here with the very unimaginative Roxy10 I always use a variation of Roxy in AC so when making account I just used the NL spelling and added 10 cos it’s both my birthday and my sons
I try to avoid it as much as possible. I really don't like it when I come up with something cute or unique only to find out I can't use it because apparently there's a parallel universe.
If I have to, I usually go with the pokédex number of a favorite Pokémon, or if I'm not feeling creative that day I just stick with my bday.
People do it for several reasons. Maybe the number has some significance or they just like how it looks. I personally don't like it but it doesn't bother me seeing numbers on other people's usernames.
I used to have numbers in my username on here because I was reusing one I had come up with in 2008 on a different website. There wasn't really a good reason for it, honestly.
when I've used numbers it was because of a username I really wanted but was already taken or the numbers I used mean something to me or refer to something that I admire.
Some workplaces or educational facilities I have been at required numbers in usernames as well. (heh my age is showing a bit here.....)
I always use a variation of Roxy in AC so when making account I just used the NL spelling and added 10 cos it’s both my birthday and my sons 
) mainly for one of two reasons:
