I beg to differ on beths level of creativity.
RE the book: there are 200+ year old 'factual' books about vampires, witches and all sorts IRL. Would you take everything you read in them as gospel? Only if you didn't know any better.
So why, in a game that tries it's utmost to reflect a living, breathing world, should we think that a 200+ year old book is, or even was, accurate.
Ok Bieltan, look at this from their perspective.
"Ok, it's time to create the Volkihar, after all it is Skyrim."
"Should we follow the lore-based facts we already provided about them in Oblivion?"
"What? Are you mad?? That'd make ZERO SENSE AT ALL!!"
"....wat? How so? This is how we said they would be."
"Yeah but it's been 200 years! Obviously that would mean they should be COMPLETELY DIFFERENT. Look at how much our orcs evolved in 200 years! Look at how much our Argonians evolved in 200 years!"
"....Not at all?"
"SILENCE!!!!!!"
"....So what are you suggesting? How should we make them?"
"EXACTLY like the Cyrodiil strain."
"...One, that makes less sense and two isn't that just an excuse to use less resources and copy-paste the existing vampires we have into our next game?"
"Well then what do YOU suggest, smart-guy?"
"Something new? Perhaps...something that follows the lore?"
"SOMETHING COMPLETELY NEW?!!"
"No, I mean something in lore that we haven't done be-"
"BRILLIANT! How about Vampires EXACTLY like in Underworld?"
".....WHY? That's a blatant rip-off of another series and we've left no indication for the Volkihar to be like that!"
"Isn't it obvious? All forms of vampires, if left to their own devices for over 200 years, evolve into stereotypical Underworld vampires. God, didn't you ever take biology in high school?"
Do you REALLY think that's how it went down? That they conciously decided it's illogical to make them like....yknow like they used to be?
I'm sorry, but that just makes zero [censored] sense. Stop making excuses for what's quite obviously a decision driven by profit.