I personally have yet to see one where any of the women, either playing or DMing, are unattractive. Did all these attractive women suddenly decide to go public with their gaming? Or did some of them have no experience prior, but thought "hey, men are willing to watch me play this game and spend money on subscriptions" or whatever and are simply using their looks to make an income like so many women have throughout human history?
Well, why don't we take a look at some of the most popular show rather than speculating about the women's motives.
Critical Role - All of the players played in a private game for 2 years before it was ever streamed.
Dice Camera Action - Both female players have played D&D for years.
High Rollers - This is a game run by the Yogscast - one of the female players was one of the biggest female streamers they had, played D&D a long time ago and was coming back to it. The other is the partner of another player, and has played D&D before.
Rollplay - There's a huge variety of shows and players on this channel. The main show I watched had a rotating cast of other streamers, was a mix of men and women and a lot of both sexes were new to D&D. Some came back if they enjoyed it, some didn't. The women on the other shows that had a consistent cast had usually played RPGs for years. This channel was also founded way before D&D streaming was popular, so their was little to gain from showing up with a pretty face and hoping to make some money.
I'm sure some women did decide to go public with gaming as it became popular. I know for sure that some were new to D&D, but to assume their motives were entirely based around money rather than "this sounds fun" is a little unfair.
You're right in that the streams that are popular do tend to have attractive people (not just women, have you SEEN
Travis Willingham?! ) and also a mix of genders. But I think this is part of why they become popular - the games that you want to watch have a diverse cast rather than a bunch of dudes.