Yeah, I wonder if that’s perhaps the result of basically stapling the old game engine onto UE5 in order to preserve the core gameplay. Back when Oblivion was first released, multicore CPUs were incredibly rare, so it’s likely the engine was not built to take advantage of them. But ever since then, most of the improvements in CPUs have come in the form of adding more cores rather than increasing clock speed, and it’s by no means trivial to convert single-threaded code into multi-threaded. Most likely it would require a complete rewrite, which they’d probably want to avoid in order not to introduce more bugs.

But of course, it could also just be UE5’s fault, since even a single core on a modern CPU should not be slower than a 2006 model.