Yes, I think this is how some people see it; a professional author is getting a tangible benefit of cash from their work, while an amateur author's only benefit is audience reaction. So a negative reaction, while appreciated by some authors, is a slap in the face to others.

I also think there's an element of fandom being a hobby - criticizing a pro sports player's game is a way to participate in sports fandom; but watching a couple amateurs playing a tennis game at the local club and explaining aloud what's wrong with their backhand is considered fairly obnoxious.