If we allow the CPU to enter standby, this will interfere with intervalometer and any other ML tasks that you may want to run with display off.
Sure, it is possible to disable the CPU powersave only when needed. However, solving it would have quite a bit of added complexity (identifying everything that one may want to run with display off, and making all these tasks powersave-friendly).
It would introduce a new class of bugs. Examples:
- you implement a new feature, let's say a custom bracketing sequence; if you forget the powersave guards, it will only work reliably with display on, and the behavior will have a high degree of randomness with display off.
- let's say you forget to enable CPU powersaving after using some feature; result: a bug that can only be identified with the ammeter.
The benefit would be... 20 hours in standby instead of 10 (5D2). Or, 25 instead of 16 (60D).
If you actually use the camera to take pictures, the difference will be much smaller.
Worth the effort?