Summit is A reason not THE reason.
Rare has done a good job trying to put out content at a reasonable pace (I think 2 months between updates on average). So, it can only get better from here.
Another reason, sales on MS game passes for Xmas/Winter. People that play the game from the pass. They play. Get bored. Update comes out. New pass. Play again. It is the number 1 game for their pass, I think.
Twitch is advertising. I don't mind Summit doing what he does because he is not hacking or breaking game mechanics. He has a play style. That's all. And some newbies are learning and trying to sneak on people's ships. It has happened a lot to me and I thank him for that because more people want to play the game and in different ways.
I still meet friendly people. I play on a fleet with a lot of people that have been playing since day one.
You get people that are hardcore (since day one).
Moderate (on and off each update).
New (Just recently purchased the game. Learning new mechanics).
There is no data out there but due to the Christmas season and the Shrouded Spoils, it probably brought in a lot of people. And now, Rare has an opportunity to keep players interested with the Arena (because arena based games are the rave now, right?!). Rare has a method to their madness. If they succeed, MS will pool more resources and adventure mode will be that much better (and they are still working on Adventure mode too right now, so).
The updates and the game are what people are playing for. Streamers just advertise and entertain.