I believe the answer is that the demonrats have been programming their splinter groups for decades that they are unified and cannot refuse coalition with each other. They are all co-victims, all needing gummint, and specifically demonrat-controlled gummint, to protect them from the normal -- speaking literally -- majority. To me it's surprising that has worked as long as it has. A lot of the splinters have no common ground with each other and no real reason to support demonrats.