where did the centaurs from daggerfall go? it's as if they were just wipe off the face of TES lore

I could give you a lot of explanations but the most logical one is that the Elder Scrolls series was somewhat "rebooted" after Daggerfall. Redguard and Morrowind changed a lot of things (in my opinion for the better) about the atmosphere of the world and its lore. As a result A LOT of enemies we saw in Daggerfall and Arena were changed (daedra lords became dremora, argonians aren't human) or completely scrapped. I'm not sure if centaur have been retconned from The Elder Scrolls, but I wouldn't be surprised if it's another of those things that were forgotten during the transition.

Centaurs are still mentioned in both editions of the PGE. As such I would still say they are there, we just haven't been to an area with them.

That said, ESO misses a lot. Like... Basically everything not already defined in main TES games. Even then, Morrowind and Skyrim are more than a little bland in comparison to the TES games.

They were all surgically separated, and then made into the Legion Riders in Oblivion.

My guess? They did not want to model a 3d centaur.

it was not rebooted, rebooted means starting over from scratch, the fact Oblivion clearly mentions the Imperial Simulacrum shows it was not rebooted

That's why I put rebooted in quotes and prefaced it with "somewhat". I wasn't being literal :]

heres an even more radical theory maybe they're just native to high rock.

Centaurs are both in High Rock and Valenwood. I do hope we seem the Centaurs return, like the Harpies and the Lamias in ES:O. Thogh Hippogriffs, Basilisks and the Faeries still need to appear. I guess you could say that the Nereids are in some way Faeries, actually, what is the deal with the Nereids? Where do they come from? I think they are worshiped in Valenwood.

ding ding ding

They live in Valenwood for sure.

Centaurs are like Giants. They are only native to specific areas of Tamriel. I believe High Rock and Valenwood for Centaurs. (High Rock and Skyrim for giants).

Same thing with a lot of other creatures. (Guars, Nix-Hounds, etc are native to Morrowind. Apparently Nagas are native to Black Marsh. And so on).

Argonians are only human-like in Arena. (Human with scales). They were more lizard-like in Daggerfall... Actually, they looked highly similar to the Argonians in Morrowind except 2D instead of 3D and had a different shade of green.

Well, all of vanilla Morrowind's creatures are uniquely created for TES apart from giant rats and skeletons, so it's not that surprising that they weren't in that game. I don't think they would have 'fitted' into Skyrim, but they could've worked in Oblivion's high fantasy aesthetic - they're just one of a few creatures that hasn't made it into later games.