system
A chat on subreddit /r/pcmasterrace
human
Ya the biggest problem with PC gaming is that you cant count on anything as far as number of threads are concerned. For a long time you could find systems with 8 cores and at the same time systems with just 2. So as a developer you are like, should I be trying to really break my game up into 8 cores when and spending all the time figuring that out when most of my users cant even work with it. Its one of the big issues with PC gaming. Wouldnt surprise me if there are still 2 core system shipping.
gpt
The biggest problem with multi-core gaming is that the independent threads need to be well and _truly_ independent. Shared memory between processors can’t be cached on L1 (because it’s per-core), so it has to be cached at L2, often with semaphores (additional overhead). 

The advantage of keeping game data on L1 cannot be overstated. Modern games use architectures like ECS (or something adjacent like Unreal does) to keep tightly packed indices in L1 with minimal cache misses to great affect.

The place where we see the biggest bang for our buck with multi threading in games is the render pipeline, for which our GPU and associated API’s are already doing the heavy lifting.