It’s cpu limited because you can’t always parallelize logic based calculations which depends on some previous result or modifies some common data in memory. Those sequential operations needs to happen on a single core. If they are forcefully spread over multiple cores, the game will perform even worse because of thread synchronisation. That’s why MSFS tries to use as many cores as it can. But only one or two of those cores runs the most intense sequential operations. And those cause the bottleneck. Even if MSFS uses 16 cores, if those sequential operations cannot be parallelized, then those one or two core will be always fully utilised but the rest of the 14 cores will wait for those to cores to complete certain tasks and remain underutilized. Now if we try to run this on a quad core system, then we may see all 4 cores being fully utilised because those calculations which were spread over the 14 cores in the previous example will run on only 2 cores in this example. And that’s why they will have more utilisation.
Apologies for the programming lecture.