There is only so much that can be multi-threaded, beyond that the overhead just slows things down (and can cause bugs)
More simulation type games (city skylines etc) can multithread more (generally) while your standard shooter has much less that it can do (unless you have AI bots etc)
My point here is the developer managed to split the load evenly between 8 threads. How come they cannot do it for 16?
The keyword, evenly, means all 8 threads are at 100% while other 8 threads are at 1-2%.
You’d need to look at the actual implementation, it’s hard to speculate from a tiny amount of data. What game are you referencing?
And as someone who has done multi threaded programming I can tell you that for games it is unlikely that they can just add more cores. You need work that truly can be split up, meaning that each core doesn’t needs work to do that doesn’t rely on the results from another core
Graphics rendering is easy for this and it’s why gpus have a crazy number of cores. But you aren’t going to do graphics compute on the cpu
For that number to be 8 though suggests that there’s just a “number of workers” variable hard-coded somewhere.