The Docker daemon (likely the HyperKit VM) on the Mac has a tendency to burn CPU cycles, even when there are no containers running. It's pretty common for it to sit at 10-20% of a core all day, and sometimes gets pegged at 100% until you quit.
There are countless closed issues in the GitHub issue tracker [1] for similar issues, but the symptoms don't seem to go away for me or many of my colleagues.
It's been a pretty awful experience on Mac for a long time, so any competition is surely welcome.
[1] https://github.com/docker/for-mac/issues/3499
