Because “man” can refer to:
male vs. female
older male (physically) vs. younger male
maturity vs. immaturitty
whatever you define as ‘manly” vs. “unmanly”
or a male dragon.
I am one or more of those things, but not necessarily all of them. since I wasn’t sure in what sense it would be read, I decided to put it in quotes to signify that I wasn’t necessarily a man according to the readers perception of “man”