It has to do with how you're remembered, though. Names like 5hift are much easier to recognise, quote, and refer to, whereas others such as XxxxK1LL4Z24!%3567xxXxxZZZ aren't. Like passwords. People are much more likely to use Passw0rd rather than suggested passwords like 2NQUILYR!8034XO.

Besides, the former is more unique and doesn't contain five hundred numbers, making it seem more important/original and therefore is more memorable.