It's a subjective thing, there's not really any practical value in wearing baseball caps anyway except for keeping the sun out of your eyes, which other types of hats do better anyways
It's mostly down to the whims of pop culture, in the 50s they bent their cap brims and anyone who left theirs flat was a dork, so then they started manufacturing curved brim caps and everybody was wearing those. I don't know whether the baseball people ever switched over, but now the flat brims are back in style and people with curved brim caps are seen as out of touch fashion-wise and possibly republican, and for their part they see people with 59fiftys as dumb or tacky or whatever. And for every emo goth kid (for example) who thinks my hat is dumb there's someone else who thinks his boots with 20 belt buckles up the side are dumb
tl;dr fashion makes no sense but everybody does it