GL, from my very brief look into this earth-shaking matter, it seems the issue is not the weight loss, per se, but rather how it was done and how it was conveyed to the audience. There is widespread belief that SJ used gastric bypass to lose 150 lbs in one year, but she alternately denies or will not discuss doing so.
There's also the issue of plugging businesses on the show or her website that gave her free services for her wedding.
The bottom line, the story goes, is that the brass felt she was "losing the audience".
I haven't a clue how true any of this is, but their might be more to this than reverse lookism.
One takeaway here is that regardless of what official feminist orthodoxy may say, weight seems to be a very important issue to many women.
p.
You might well be right. I don't follow the show. I was relying on the explicit quote from Walters in the AP article that one of the reasons behind the firing was that Star's weight loss "had turned viewers off."