Apparently the reason is because Sega wants Rovio to act as their go-to studio for mobile games (similar to what Nintendo has going on with DENA, though Nintendo doesn't outright own DENA), but this timing is interesting given one could argue Rovio isn't quite the powerhouse they were when Angry Birds was by far the biggest game on mobile (and they even caused controversy recently when the OG Angry Birds, a $1 paid game with no microtransactions or intrusive ads, was delisted from Apple's App Store and the Google Play Store last month in order to try and drive all Angry Birds traffic to their free-to-play games that are full of microtransactions and ads).
The only thing I'd be concerned about in regards to this situation is I hope Sega doesn't take the route of "revive an old IP as a mobile exclusive f2p game" with whatever they have Rovio work on as I know damn well a lot of people would be pissed if the first new Jet Set Radio or Space Channel 5 game in years was a microtransaction filled mobile game.
