Holy crap, this thread is flying today.
Of those, only Conchata Ferell could really be called overweight and even that is pushing it. Of course, by television standards they're morbidly obese...
Since when is Rosanne Barr not overweight? That was half of her characterization, especially in those days.
Anyway, I've been trying to think of some "unattractive", if not necessarily fat, women in TV and movies. I came to an idea after thinking of some of them. Along with Rosanne, there was Katie Sagal's character on
Married With Children. Katie Sagal is not herself "ugly", but Peg Bundy was definitely supposed to be after stage makeup; that was the point, she was a preening housewife who thought she was attractive but really wasn't. That show was already making fun of the "Ugly Guy Hot Wife" dynamic years before it became the dominant style of sitcom.
In movies, there was any role Ethel Merman ever played, most especially in
It's A Mad Mad Mad Mad World, with a similar character. Her entire plotline revolved around her being a terrible and terribly unattractive person, with slapstick meted out against her for being a shrew. More recently, there was
League of Their Own, where several of the characters are specifically described as "ugly", and were cast as such within the confines of Hollywood casting (even ugly men are never really ugly). Admittedly, this whole effect is part of the what the movie was about, but you still had unattractive female actors.
In thinking about this, and how these examples are all at least twenty years old, I honestly think there's another factor in why you almost never see unattractive women in media, and I know I'm going to be crucified for it. This thread has a lot of what I'd call "rational feminist" opinions, namely that a reasonable portrayal of what are supposed to be real people should include some unattractive people. Showing only attractive women is sexist, because it sets an unrealistic standard. I think some producers cast that way with an expectation, and not undeservedly so, of being hit by the "radical feminist" opinion, which instead treats any portrayal of women as less than ideal as sexist.
To what extent I don't know, but I really do think that factor is there. If you tried to produce and release
It's A Mad4 World today, every magazine in the country would call it the most hideously misogynist movie produced in thirty years for how much they insult and beat up on a respectable female character like Mrs. Marcus cum Ethel Merman. And they would, technically, be right.