In an honest answer, they find the people they name themselves after cool, from what I can gather.
It'd be comparable to people who make their avatars/names out of things they like, instead of just youtubers.
A few examples being fandom avatar or pics/art they like/pictures of ponies for bronies?/pictures of furry creatures for furries?/etc.
Basically, nine times out of ten, it's them naming/displaying themselves based on the things they like. Perfectly natural, however annoying/odd it may be.
the difference is naming yourself after a fictional character isn't naming yourself as an active and popular youtube channel, and then none-the-less acting like that person and saying they're them.
(e.g., this guy named rubberfruit. go on. he won't give you any proof but he insists it's the real one!)