Because they protect the Emperor, or rather, "did" because the bloodline is over. However, a better answer is that they have existed since the Akaviri came to Tamriel. Akaviri and the future generations on Tamriel kinda committed race crimes against Elves, especially snow elves. Genocidal acts against snow elves (There are one or two left). Also, the Akaviri, and the Empire they create later, kinda conquer most of Tamriel and therefore fucked over the old, Elven Dominant Empire that existed then. Thalmor promised to rebuild that Elven empire in the form of the Aldmeri Domnion. So, even though the Blades are not directly Akaviri anymore, and the bloodline (Septim) is no longer, AND THERE'S A DRAGON BLIGHT GOING ON!... Thalmor still want them dead for possibly ruining Elven progress for centuries.
They're tasked with guarding the Emperor or originally, Talos, so long as they exist they'll treat Talos as a god, so they're incompatible with fucking Elves. Thalmor are just butthurt Nords get one of their own to ascend to Godhood, while Elves suck at doing most things. Shouldn't have stopped with the Snow Elves. Should have kept killing them. Elves suck anyway, their master plan when the Humans first came to Skyrim their action was "Shit, these guys repopulate fast, let's kill off the only city they have here.", "That's a great idea! It's not like they'd ever return with a burning vengeance to wipe us out completely and make them have an incredible distrust of all Elves from now on". Moral of the story don't fuck off Ysgramor or he'll wipe your race out...
Daedric boots... i can only wonder at what they were used for How dare such filth defile the Reclamations I WILL KILL THEM ALL, FOR BOETHIA! View: https://www.youtube.com/watch?v=F0zb5S9DGYQ Also you clearly don't understand the High Elf mindset They were literally gods until Lorkhan came and fucked them over causing them to be stuck in mortal bodies. Then they kinda realised they need to kill all men to return to being gods Then Talos massacred the Isles with the Numidium. That was within recent memory for most High Elves
