1. Saturn mostly failed in America. Sega of America refused to bring all the good games that were Japanese exclusive and they priced it at $400. Saturn in Japan had a lot of hit titles like Virtua Fighter 2, Sakura Taisen, and the Capcom vs. games. Plus, SEGA had Segata Sanshiro played by the original Kamen Rider1. Sega was in a poor financial situation after the failure of the Saturn in most of the world.
2. Big publishers like EA felt burned by the Saturn and decided not to release games for Dreamcast. Maybe not everyone plays Madden, but Madden definitely sells systems and that hurt Sega.
3. The launch of the PS2. Yes, there was a lot of buzz for the Dreamcast, and it did have a successful launch with lots of great titles. But that buzz was killed by the announcement of the PS2. Since Sony was the clear winner of that generation, lots of fans would obviously be on board for their next generation offering.
4. DVD. Even though DC games generally looked quite a bit better than PS2, the PS2 did have a DVD player. It may seem trivial now, but seven years ago, DVD players were still expensive, so the PS2 was the cheapest way for a lot of people to jump onto the format. In those days, that definitely hurt the Dreamcast (and the GameCube).
Any talk of Dreamcast not having enough titles is silly. There were plenty of great titles that came out during its lifespan, many of which have been ported to other systems. It was definitely a system for the serious gamer, the likes of which will probably never be seen again.
2. I would talk about what I don't like about EA sports, but you'd have to be a fan of the Hajime no Ippo PS2 gaming series to understand my argument against them. But NFL2K was ahead of its time.
3. Yeah, Sony already confirmed DVD playback and backwards compatability with improved graphics and loadtimes with PS1 games. DC was hurting because no good games came to America on the Saturn.
4. I know a DVD system for DC was only released in Japan, same with Gameube sadly.
But DC was a great system for 2D fighters. I still call Shenmue the greatest game of all time. Dreamcast still caught a cult following but Sony already had the advantage with the success of PS1 and Sega was at somewhat of a disadvantage due to the bad mishandling of Saturn.
Saturn was also a great sytem but it was a pain to program with (it was also a pain to program the PS2 at first but things eventually got easy) and like I said, the only great Saturn games were moslty Japan exclusive which also became DC's fate to some extent.