Most things with CD tried to be backwards compatibility, most things with cartridges not so much.
That's not really accurate. Sure the Playstation line was Backwards compatible up until half way through the PS3's life span but none of the Sega Disc based consoles were BC. However Sega's Genesis could play Master system games with the appropriate adapter. (the adapter was really only there for the slot to accept the cartridges). Also the Atari 5200 and 7800 could play 2600 games. The gameboy's were almost all backwards compatible through that entire lineage and now the DSs are are almost all backward compatible through their lineage. And those are all cart based. The Wii could play GC games but the WiiU could play Wii games but NOT GC games. All of Microsoft's consoles were only semi-backwards compatible since it's really just emulation and support was added on a game by game basis. Then you have other weird stuff like the Super Nintendo could play Game Boy games and the GameCube could play GameBoy Advanced games.
My point being that there's no general rule when it comes to this stuff, the compatibility from generation to generation is inconsistent since support just comes down to a cost-benefit analysis for whoever made the console.
The final nail in the coffin is that SEGA's first party development teams were just kind of bad at their jobs.
I beg to differ, Segas 1st party titles during the Dreamcast era were at the top of their game and produced titles and franchises that are STILL making them money re-selling on different platforms as many of them have become cult-classics. Crazy Taxi, House of the Dead 2, Jet Set Radio, Panzer Dragoon, Virtual On OT, Space Channel 5, Chu Chu Rocket, Shenmue, etc. Even their flagship driving game Metropolis Street Racer when on to spawn 4 sequels in the Form of Project Gotham Racing and was the Xbox's flagship driving game until Microsoft introduced Forza.
The Sonic games released on the Dreamcast were actually rated fairly well and fairly well received by fans. Most consider them to be the first 3D Sonic titles made by Sega that didn't suck.
Sonic Adventure on GameRankings scores an 86: http://www.gamerankings.com/dr...
Sonic Adventure 2 scores an 89 on MetaCritic: http://www.metacritic.com/game...
Take an astronaut to launch.