The title pretty much.

I'd like to explain my thoughts a bit more. Why were Vampires in Oblivion have more purposes to use than Skyrim vampires?

Vampires in both Morrowind and Oblivion could use melee and other abilities; they also had a broader range of perks such as resistance to weapons and had special stats towards strength and other special stats. In Skyrim, we get vampires for players who are devout magic users....apparently. Yet, devout melee users who like vampires......won't really find a lot of those special vampire perk skills very useful since they're running around like Conan or Hercules hacking crap up.

Why did Bethesda decide to do this in the first place?

I found vampires in Oblivion to be more fun considering I could use a range of abilities.

I have no problem with the werewolf perk, but it would be nice had they kept some things the same as far as vampires go.

I suppose there is nothing wrong role playing as a vampire mainly doing melee and enchanting is there?

The reason for the nerf of vampire I think is that there is just not as much use for vampires in Skyrim. Skyrim has never had a problem with them and so they were a key part to having in the game but they are still fun to play as. I personally don't like having my blood boil in the sun but I couldn't pass up the opportunity to be a vampire Argonian leader of the Thieves and Dark Brotherhood. The shadows are your domain and anything unlucky enough to venture to the darkness will discover that you are the noise that goes bump in the night.

I was a vampire for a time their abilities were not bad but.. Well I was attached by vampires in my first play through of skyrim and I didn't realize that I got vampirism I think I became a full vampire when I reached the graybeards and they killed me I didn't really know what to do it was still early in the game so I decided to leave the grey beards alone...instead I spent my days trying to cure myself but I ended be comeing a werewolf instead.I think that well vampires had a general purpose it was to really give the game a whole other dimension.... think would have skyrim been better with or without vampires?

if you mean more purpose by being able to jump over houses or even mountains and swoop away every enemy npc by just putting on their ugly face

i m glad that abuse has stopped

even vanilla skyrim vampires are pretty powerfull compared with normal characters and with time and experience they pretty poxerfull and i am not even going to mention the vampire lords

i think vampires now not only are more immersive than before and wtill a very viable option and when properly build a very very powerfull build even when it can not jump over building or even mountains and even when it actually has to fight enemies

Vampires were very good I loved them..

Vampirism, if used correctly, can be the most powerful class in the game! Restricting yourself to night isnt hard to do and as a vampire lord your drain spell (after being leveled up completely) is OP

since when could a vampire jump over a mountain?

Normal Vampire Form is suited towards Stealth characters, especially Nightblade types. Vampire Lord Form is more suited towards Mages. Werewolves are suited towards Warriors.

Since Scrolls of Icarian Flight...https://www.youtube.com/watch?v=rFiq_5ZTD9I

I am more than aware of the Scrolls of Icarian flight, but they weren't a Vampire thing, anyone could use them

I suspect it's to provide a supernatural form for stealth characters and mages, as opposed to the werewolf's strictly-warrior form and buffs. If they tried to make them more general purpose, it might've made them more OP.