Aside from the fact that none of the mainline pokemon games (not including stadium) are available, or the fact that Caastlevania has a collection for all the GBA titles (but 2 on GameBoy still wound up on Switch Online for some reason), so you can point to that as to why they aren't on the online catalogue (MegaMan and X are also included in that), we have:
- NONE of the F-Zero GBA games,
- SML 1 and 3 are missing along with Wario Land 2
- Game & Watch Gallery 1 and 2 are missing along with 4 on the GBA
- We get Quest For Chamelot.... a fucking 1998 Warner Bros animated movie that barely anyone remembers but yet no other movie-license game is chosen? Nothing from Disney... which had more memorable games. Nothing regarding any of the Looney Tunes, which is more of a recognizeable Warner Bros IP than anything else (not counting capeshit)
- None of Sonic's games for the GBA
And that's just off the top of my head.