My opinion is that it's the gradual turning of vampires from [censored], vicious, highly metaphorical and symbolic predators to kind of pointless "people who can't walk in the sun and drink blood" bullcrap from teen fiction. Gah, I hate teen fiction. Only problem with working in a library, really. Anyway, it's happened everywhere else, why not strip thenm of thier psychological awesomeness in videogames too?

Divayth Fyr used magic to create his daughters. Why shouldn't a vampire use magic to cross the boundaries between mortal and vampire to successfully create an offspring?

Because Divayth Fyr is one of the most knowledgeable beings in Tamriel, and has lived as long as the living gods of Morrowind, and blatantly tells you he could clone his daughters because of his research with the Corpus disease. The collective minds of all vampires do not come close to Divayth's knowledge. Plus, most are not too concerned with creating babies, instead they bite to reproduce. Their entire existence came to being from the daedric prince of schemes, [censored], and corruption; they are a complete mockery to life. And I do not think there is any potion or spell that'd bring any vampire's seman/egg count back up.