CPU has been a bottleneck for CoC/Anomaly forever since Xray was originally made in that time when people thought super fast single core processing was the future. So GSC optimised it for that idea. Instead it turned out clock speed has pretty much flatlined since then and multithreading was the future. Plus it doesn't help that all the offline simulation of what the world is doing in the background offsceen is incredibly CPU heavy.

STALKER modding is absolutely crazy, not quite as large as Skyrim but also harder to quantify since in addition to the by-now massive Anomaly scene there is also a massive scene that's still spread out over other older offshoots, particularly in eastern Europe. They're very big on modding and remaking the original trilogy there (STALKER is huge there in general). Hell, I actually have Oblivion Lost Remake installed and ready to go, which is a fan-recreation of the original vision of Shadow or Chernobyl, recreated from design documents and early dev builds that have been leaked. GSC famously had to cut down their vision massively to get the game out the door and OLR 2.5 has been described by many as the closest thing we're ever going to get to what they actually wanted to make (Oblivion Lost was the original title before it became SoC).