Baby boomers (named after the post war baby boom that created them) started it by calling the generation following them "generation X". Then millennials were gen Y for a while before the millennial rebrand after the turn of the millennium for some reason. Gen Z got the nickname zoomer pretty much because it rhymes with boomer. Then we ran out of letters because the boomers decided to start at the wrong end of the alphabet, so we're doing the Greek alphabet now. Thus gen alpha, who haven't been around long enough to develop an identity resulting in a catchier nickname.

Given generations seem to be about 15 years or so, the line for gen beta kids is just around the corner I guess