TracyDMcGrath M.U.S.H.A., Castlevania Bloodlines and Contra Hard Corps aren’t Sega games, and thus aren’t on those compilations. (CV & Contra are in the recent franchise collections, as well as the Genesis/MD Mini, and M.U.S.H.A. was also on the Japanese MD Mini.)
Strider’s also missing; Sega owns the port but it’s a Capcom IP, obviously. (Again, it’s on the Genesis Mini, and the original arcade version’s on Capcom’s own arcade game app.)
Ecco the Dolphin’s missing from the console versions of the collection due to rights issues from a few years back; it’s still in the Steam version of the collection AFAIK and it was also on the Genesis Mini.
If Sega (or whoever’s picking the games) wants to go deep, there are plenty of surprises still out there that haven’t been reissued ad nauseum, but I’m not confident about there being any real surprises.
tomjonjon My understanding is that it’s partly due to an existing licensing deal they have with an international controller manufacturer.