Fan speed slightly decrease under load. Why is that?

I doesn't bother me but when I have set the fan speed to max from Predator Sense the fans' speeds get to CPU fan - 3800rpm, GPU-4300rpm and 3rd fan - 2800rpm. While running a game for about 10-15 minutes the fans' speeds decrease to CPU-3600rpm, GPU-4100 and 3rd fan- 2000rpm. I contacted Acer about it and they told me it is a power management, that my system draws too much power and therefore it gets re-allocated to GPU and CPU, decreasing the power going to the fans.

I don't think that is the case, because even after stopping the game the fan speed stays as it is and doesn't increase back as it was before and the only way to fix it is after reboot. I went in power management settings and set the cooling to be constantly active while plugged in and while on battery, but it didn't fix the problem. I also looked in the BIOS and didn't find anything.