Honestly, because I'm lazy. Maybe I'll use 'they'. Maybe I'll use 'he'. Maybe I'll use both. If I'm not given the gender of the author, I'm just going to write

Honestly, because I'm lazy. Maybe I'll use 'they'. Maybe I'll use 'he'. Maybe I'll use both. If I'm not given the gender of the author, I'm just going to write what sounds right rather than take the time to make it gender-less. It's not like I would blatantly disregard the author's gender if it was provided, though.