system
A chat on subreddit /r/me_irl
human
This is more or less it.  Most people aren't trying to be transphobic, they're just using pronouns how they've been used forever.  If I see someone who looks like a girl, I might say something to my friend nearby "What do you think she's doing over there?"  I'm just using 'SHE' as a pronoun because it conveys information to my friend that I am referring to someone who, at the very least, *appears* to be female.  This way when they look over there, they're going to know I'm referring to a female-presenting person in case there are multiple people in the direction I'm referring to.  


Pronouns normally carry a small degree of information in them beyond just preference, but once someone's preferred pronouns get muddled in with it, there's no longer information in that pronoun, it's just another name/nickname.
gpt
I still call a mixed group or even a group of women "hey guys" and no one cares.