Sort the performance would mean a complete overhaul of the current engine. I'm all for it. ZOS probably isn't.
Sorting the engine would be a long term investment, with a very unsafe investment return. There simply is no guarantee that the money spent on a new engine (to sort the performance) would produce a net gain. Especially when the majority of performance issues are related to Cyrodiil pvp, where money doesn't need to be spent by players in order to enjoy the game.
The other part of the community is the PVE side of things, where performance only really matters to the "top tier" players (competing for a better score based on how long a clear takes and performance becomes a huge factor). Once again this group of people is a minority (like the pvp vet's) and an improvement of performance would most likely not result in a net gain for ZOS.
All this is tied to what the game is on a more fundamental level; easy access for everyone.
A progression would mean many players in the current community (not the community ESO had in it's early days) would be locked out of content. Not only that, but on a competative side of things many people would find themselves disadvantaged because they don't have the "time" to invest into becoming "better".
There are ways around this, however, but the majority of players in these categories are completely unaware of the games fundamental flaws in order to have a proper discussion about it. The other group of players doesn't have a progression mind set and thus the issue doesn't apply to them, and this is the majority of players which ZOS is "taking care of".
Simply put, most of us caring about getting better at an end game stage is playing the wrong game.
("Yay!" for being so positive) ^^
yes when rebuilding the engine make it do action combat kthanks
"Civilized men are more discourteous than savages because they know they can be impolite without having their skulls split, as a general thing.”
― Robert E. Howard