The longer we can keep shoving in the exact same selection of crunchy res 8 bit roms we've been doing since 2002 the longer we can keep trying to convince ourselves and the consumers that any of them are actually good!

@starleaf I think the top and bottom of it is down to that they weren't released in Japan (and the US for 2, Chaos, Mean Bean Machine and Spinball, not counting the Brazil only Sonic Blast that Tec Toy hacked up). Sonic Team weren't really aware of these games as for a while they weren't to their canon as all of them were done by outside teams (Ancient, Aspect, Arc System Works, Minato Giken, JSH, Sega Interactive for Spinball, Compile for MBM). Not entirely sure but I think Sega of Japan themselves and Sega Europe handled the Master System stuff. I think the last time these games were on were via the Virtual Console, if not then their original releases.

Coding a Master System emulator isn't really that much extra work... Well considering a Game Gear can actually run Master System cartridges with an adaptor plus a very few Game Gear games were actually designed for the Master System with the same resolution (Castle of Illusion, Chase HQ, Out Run Europa to name a few).

I'm curious why they didn't go and include the official SMS releases for the games that had them (1, 2, Chaos). was it consistency reasons? did they not have/want to make a Master System emulator?

No, it's on-disk. It's an enhanced release, pretty sure, but the one I have has them.
...if only it had the remaining Mega Collection Plus and Gems games... and Chaotix... and Saturn 3D Blast... and SegaSonic arcade... and Jam world...

dlc games?