Actually this makes complete sense to me, but I might be entirely wrong too.
If the simulator is having a burst load of assets from the game folder, while at the same time it is trying to cache-in or cache-out scenery data, you can reach a contention state limiting overall I/O. Having 2 separate drives each one on its own SATA line might give more throughput and more importantly eliminate BUS I/O contentions.
From my understanding, some SATA lanes depend on the PCIe lanes, and some of them are straight from the CPU, others from the chipset. In mixing the two appropriately with 2 drives there is a chance some systems are exhibiting better disk performance under heavy contention.
I’m thinking about this because of this peculiar bug affecting my test system for which I’ve found no reference online at all, and spent many hours to try finding the root cause and the cure:
PSA: Solution to HDD and NVidia causing Win10 System Halt with Black Screen
TL;DR: waking up the HDD was taking enough seconds to freeze the mouse and making the NVidia card failing, forcing a hard reboot.