Update 26 reversed how feeding affects Vampire stages, but there was never a solid explanation for why that decision was made. The only thing said about the change was that it "forces [us] to embrace [our] dark side to retain [our] most deadly powers."
"A CURSE AND A BLESSING"
"With Update 26, the team has also changed the way you must manage the four stages of the blood curse. You can increase your stage by feeding on NPCs, but they also slowly decrease over time,
forcing you to embrace your dark side if you wish to retain your most-deadly powers."
https://www.elderscrollsonline.com/en-us/news/post/58225
But why? It used to be that the longer a Vampire went without feeding, the deeper into Vampirism they went. That played better -- feeding would bring us closer to a regular form, but the longer we went without feeding, the more the hunger set in and the more of a Vampire we became.
Post Update 26 reversed that and made it so if we don't feed, our Vampirism and thirst for blood lessens (huh?). That, plus the way that passives and stages are set up (ramping ability costs for other skills) means that for most of the game play in ESO I am incentivized NOT to feed as a Vampire.
Please reverse the Update 26 changes to how feeding interacts with Vampirism stages.