Maybe growing up in a warm, costal area makes it more common, but young women just wear similar outfits to most feminine streamers where I’m from. They usually aren’t making a statement about it, it’s just hot outside and they don’t mind showing off. It’s normal.
Some streamers do embody the meme. Some focus cameras on their ass. However, feminine streamers aren’t the majority, and most of them aren’t even that sexual. On a whole, men have more viewers, with almost every top streamer being male.
Part of why the discourse around sexual streamers seems so prudish is that they don’t dominate on twitch. There are a few popular ones, but women don’t even dominate the site; there’s just more of them than in the past. Most feminine streamers aren’t sexual. People see what they want to see.
The only male streamer ever suspended for showing his bare chest was crossdresser. Masculinity is normalized, so femininity is othered.