There is a sizeable gap between "beyond a reasonable doubt" in terms of a very specific law, and things that are gross/immoral.
People keep questioning the timeline as a defense... They might not have known until 2020. It's normally against internal company policies to just look through people's DMs. It's not like someone's job is to rifle through them. They probably were made aware of it, and then took action.
That's speculation on my part, but if Twitch sat on it for 3 years, shame on them too, but that doesn't so shit for this guy. It was still not ok.
The monetary incentive was to pay out his contract so they didn't have a VERY public story about a VERY high profile streamer inappropriately messaging a minor with their service. That could be super damaging for Twitch. So they likely paid it out to try and bury the story.
I would add potato to that list. People fucking love potatoes on lots of forms.