Heh! Over the past couple of years, I have been repeatedly taken to task for RCU's being insufficiently aggressive about allowing the scheduler-clock tick being disabled. As in a handful of ticks at the beginning of an idle period.
So the sensitivity to CPU consumption is way higher than I would have guessed a couple of years ago. In addition, there are other well-known issues that arise when relying on a separate daemon in addition to efficiency. I have run into them many times over the years (make that decades), and I would guess that you have as well.
It is instructive to turn the question around. First, start with the assumption that the Android guys actually are competent in their area of expertise. Then ask yourself why a userspace daemon might be problematic for them.