The engine came in hot this gen and the early versions of UE5 were almost like an alpha version, bad performances all around, otherwise they wouldn't make 4 hours specials for a 5.5 or 5.6 engine performance improvements. Those improvements are a little late, the gen flew by. They also require high end hardware to even look good. Its so funny to see MGS 3 remake running on a Steam deck which is roughly PS4 power and it looks worse than MGS 5 did.
It just doesn't run like it looks.
But the biggest culprit is the ecosystem. UE5 is also an ecosystem. UE5 being the most documented graphic engine out there with the most tutorials with the most peoples having knowledge of because it's free, is an ecosystem that Epic have sold to publishers that they don't need the expensive graphic engineer nerds in the studio anymore. They don't need the seniority levels they had, they can just offload to cheap labour countries to save a buck. Of course the accountants in publishing houses LOVED that. So optimization left the building.
Surprise pikachu everything runs like shit.