Why do some people really not seem to like Piper?
Because she commits the heinous crime of not wanting to travel with you if you act like a jerk? Because she "abandons" Nat? These points seem nitpicky as all hell. But I'll quickly go over them both and give my thoughts.
It's established that Piper spends half her time locked up in the Diamond City jail, or as she humourously calls it "The Piper Suite." If Nat couldn't take care of herself for long periods of time, then Piper wouldn't carry on being a journalist, a job that requires her to get into trouble with the higher-ups in Diamond City and spend quite a bit of time away from home. Piper knows that Diamond City, for the most part, is safe.
The other point is weird as well. Piper is clearly established from the start as being someone who hates injustice. It's the same reason why I don't travel with Cait, because she hates it when I do nice things. Doesn't make her a bad companion, just not one tailored to my play style. But for some reason, people only take it as a personal attack when it's Piper calling them out for doing things she doesn't like.