Why on 8.1 does the processor frequency not drop to 300 MHz?
This affects energy conservation.
Not really, a processor at idle is still a processor at idle regardless of speed, yes a higher speed will consume more energy but it is pretty negligible especially when you are only talking about a few hundred MHz. You certainly aren't going to get a huge increase in standby times by lowering the processor to 300MHz and then i suspect you would get many people moaning about how their Nokia 8 is suddenly stuttering all the time.
so it was on android 7 and 8
so it became on android 8.1
bad kernel optimization
Slowing the phone down by another 218MHz is going to have just about zero effect on battery life.
My Ryzen 5 at 3.4GHz draws 14.85w idle
My Ryzen 5 at 1.5GHz draws 13.90w idle
A 1900MHz drop in speed saved just under 1watt in power.