OS4 Classic, why disable the 68k ?

[psxphill]

The CPUs most definitely do run in parallel.
 
I don't know who invented this nonsense and for what purposes, but it is not true.

I just think a lot of people misunderstood the context switch problem as parallel processing wasn't mainstream at the time. Using a real 68k processor was a bad idea though.

[psxphill]

when the P5 cards were designed, the 68k was mandatory for running a 68k AmigaOS.

There is no reason they couldn't have included a 68k emulator in rom to run AmigaOS.