Which is a good thing. Since many people like the barbaric animalistic vampire while others like the noble and civilized yet dangerously predatorial vampires like the Cyrodilic ones. It makes sense for them to have many different clans. Mostly being barbaric blood-drinkers.
This is why I like TES' vampirism - the clans are (potentially) infinitely flexible. And according to http://www.imperial-library.info/content/oblivion-immortal-blood...
He wanted to know about the vampires of eastern Skyrim. I told him about the most powerful tribe, the Volkihar,
... In addition to the Volkihar, there's
at least one other "tribe" of vampires in Skyrim.