EPIC was actually extremely quick in adopting DX12 with UE4 (in summer 2015 no less), but aside from Gears 4, 5 and Tactics, most DX12 UE4 started arriving only in 2020 and later. And DX12 only became prevalent due to ray tracing.
Back during UE3 games, EPIC was slow adopting DX11, only adding...