Seems like most of the problem here is you.
You hate the term gamer girl yet in the same sentence say you hate all girls that game. You then go on to say you dont like your boyfriend watching any female streamer at all regardless of what they are doing and/or streaming as you automatically assume its because she is attractive, which shows you have no trust in your partner at all.
You clearly have self esteem issues, jealousy and insecurities which you have stated but you are hiding behind it to explain your terrible outlook on the community.
Of course there are girls who sexualize their bodies for views and money. There are men that do that too and not just on twitch. On literally any platform in existence to gain followers, sponsorship, viewers etc. Humans idolize celebrities, musicians and anyone who they deem to be higher on the social ladder than they are. They all do the same thing to earn money and/or fame so its not just "gamer girls".
The post is pretty sexist really and I feel you made it just to find attention and someone to agree with you to make yourself feel better. A normal healthy person does not feel these thoughts and it is good that you can admit you have issues, but dont hide behind them with posts like this. Go to counselling and work on them.
And just to point out, I am a male.