Why I don't reply to some people:

If you message along the lines of:

"Hi"
"Hey sexy"
"Hi how are you?"
"Nice tits"
"What you wearing"
"Got 'insert social app'?"
"Love your huge boobs"
"Send copy paste DM I've sent to every woman here"
"Want to meet?"
"Send link to dick picture"

I won't reply. I've received a million of those, don't be generic.