A subscriber to a list that I belong to recently insisted over and over that the quality of writing in romance is very low. It was infuriating because other members pointed out the large number of romances that are published, the fact that there is poor writing in other genres, etc., etc., and she just would not listen. She kept insisting that there was more bad writing in romance than in other genres.
I've certainly complained about the writing in some of the romances that I've read, but I read and enjoy a few of the authors that she was slamming, and they do NOT write poorly. Some of them aren't to my taste, but I wouldn't criticize the writing because of that. Conventions are different in different genres. The expectations of the readers are different. Writing that might be considered "good" in one genre, is considered "bad" in other genres.
My guess is that what many people have a hard time with in romance is the emphasis on the emotions of the characters. I read fairly heavily in two genres--SF and romance. And you do have to switch gears when going from one to the other.
If you aren't used to romance conventions, don't read a lot of romances, then I'm sure that the degree to which the story dwells on emotions may seem ... purple. The plots may not be appealing to you. But these are the plots and the writing that readers of romance want.
I think that it all goes back to the question of which emotions you want to experience in your reading. Romance readers read to experience the thrill of falling in love, the joy of knowing that somebody else loves you more than anybody else, the feeling that you are special and important to the person that you care about most in the world. If these are NOT emotions that you want to experience, the plots and writing that are designed to create these emotions may well feel irritating and pointless. But it doesn't mean that the writing is poor. The writing may well be perfectly designed for the book's audience. It's just that you are not a member of the intended audience.
Many times when I read mainstream fiction that other people have raved about, I find the books trivial and irritating. The deep insights into the human condition that other people enjoy, I find obvious. The plots feel manipulated to produce a particular "lesson" that is invalidated by the fact that people wouldn't really act that way. This doesn't mean that the writing is bad. It means that I am not the book's intended audience.
Almost all the books that I enjoy are forms of fantasy. To me, a lot of mainstream fiction seems designed to produce false feelings of understanding and mastery over the world. To me, they seem just as much fantasy as actual fantasies--except that they aren't honest about it. I know that other people don't feel the same way. They enjoy whatever feelings it is that those books create in them. I don't.
All fiction is designed to create emotions in the reader. Different readers want to feel different emotions. Different genres of fiction are created for different audiences.
I wish people would leave it at that, and not insist that an entire genre is badly written, just because it is not to their taste.