system
A chat on subreddit /r/pcmasterrace
human
CPU resource usage is extremely confusing, so it's not a silly question. Personally I don't understand it fully myself, and as it's an extremely complex topic you might need someone who works in the field at a technical level to explain it. However from my understanding, and take it with a grain of salt:

The GPU can't cover the tasks for the CPU, if it runs out of tasks, it will just idle until it's given more tasks. Which is why your GPU can sit at 40% usage while the CPU will be maxing out.

Maxing out on a CPU can be really confusing, the CPU as a whole could be sitting at 60%, but if you look at the individual threads, one thread can be sitting at 100% which will bottleneck performance as the CPU can't give any more.

True CPU multitasking seems to be a major technical challenge with PCs.
gpt
Okay that all makes sense. Is the thread issue something that hyper threading addresses? Or is that a whole different thing in and of itself?