Back in the day, when platform games were the most common kind of game, it seemed like there was a pretty even split. Control was either binary (you start and stop instantly, and stop moving when you let go of the direction mid-air), or momentum-based (you accelerate to a maximum speed, and keep going if you let go in mid air). Nowadays, with a resurgence of indie retro-style platformers, it seems like they're almost exclusively binary. Shantae, Shovel Knight (who accelerates a little bit, but still stops dead if you let go in mid-air), and the majority of Metroidvania style games are all examples.
So, whatever happened to the momentum-based platformer? These days it seems like only platforming veterans like Mario and Sonic get momentum-based platforming. This is a shame, as it's got to be my favorite style of 2D game. I know a game is great when simply running and jumping around is fun and satisfying, but I just don't see it anymore.