>>715672903
Because the game got rebooted.
It was originally just a PoE1 expansion, basically a big engine update with an alternate campaign.
As they were working on it, they wanted to change more and more and more. Eventually they came to the point that tying it to PoE1 would make it unfeasible IF they wanted those changes. They basically came to the realization that not only would there be an incredible amount of work to get PoE1 up to PoE2 standards, but then any future content released for PoE1, even if it is just in PoE1, would still have to be developed using PoE2 in mind due to the possibility of PoE2 skills and items.

So they then decide to just decouple them. This eventually lead to them essentially restarting development minus the asset work that had previously been done. That was probably about 1.5-2 years of work. They halted development entirely about 3-4 months before the EA to put together the (really bad) end game, leading to less work being done everywhere else.
So far only their art/asset design team actually seems competent and on top of things, they even have the time to go back and port PoE1 cosmetics to PoE2.