That depends on your definition of sexual. If you have someone in underwear with the sole purpose of arousing people of the opposite sex, that is pretty sexual to me.
The microphone ear licking channels are definitely more sexual than many "NSFW" subreddits.
What actually defines porn? It's hard to say, but you know it when you see it. Spend 5 minutes watching any of the ear lickers on the front page of twitch and make your mind up for yourself. I find it hard to come to the conclusion that it's not porn.
It's sarcasm my dude. Twitch is notorious for giving female streamers a pass when it comes to nudity or inappropriate behavior, all the while banning male members for accidentally clicking on a NSFW link and it being shown on steam for seconds.
A channel I mod got a 1-day suspension because you could see the crack of a drunk guy mooning them (despite instantly stopping the stream and deleting the VOD before starting again). A few weeks before, two girls flashed them. That obviously did not warrant a ban.
Even YouTube allows more nudity then twitch.
So yes, there are girls wearing bikinis and underwear on camera, but that's as far as it goes.