They're also the only 3D Sonic titles that didn't suck. Panzer Dragoon didn't get a Dreamcast game either, IIRC.
As for the other games you mention, there's quite a few that weren't really "Dreamcast" games, but rather arcade ports - that's basically what kept the DC from having effectively zero third-party support, since they got amazing, accurate ports of what could be argued as the best arcade games out there at the time. Specifically, that relationship between NAOMI and Dreamcast also garnered them Capcom's support, and Capcom was churning out an incredible number of hits and absolutely in their prime years around that time. MvC2, SoulCalibur, Resident Evil, Power Stone, Street Fighter. Two of those were in the over-a-million group for DC (which is only 7 games), the third is one of the most popular fighting game series of all time, if not the most popular, and the fourth is one of the other contenders for that title.
Without Capcom, Dreamcast would have been truly dead to quality, exclusive third party mass-market development. There were other quality titles out there, like Legacy of Kain: Soul Reaver and Tony Hawk, but they weren't exclusive (both were ported from PSX) and as a result didn't bring enough to the Dreamcast to make it THE console to own.