It's hard to see what Docker is adding here since qemu is being run inside Docker. You could get almost identical functionality out of a bare VM image and not deal with the hassles of docker.
It's a hammer problem. Docker is the new hammer and now everything starts to look like nails.
I often wonder what it is that perpetuates hammer problems. When I look at a problem, all technologies are options. If I'm doing the work, I'll obviously try to choose from those I'm more familiar with or choose what seems like the best established/mature hammer.
It often seems like someone wants to use a specific hammer and tries to tailor/turn/reshape problems into nails. Some of it may be resume driven development, perhaps choosing comfortable technologies, etc. Perhaps hammers are the only tools they're familiar with and risk aversion in business leads us to only use our hammers.
Something is amiss because I keep seeing hammer problems and it never seems to stop.