Well I can't speak for all IaaS but both gcloud, digital ocean and even Rackspace can make a VM in less than 5 minutes which is how long it was taking to make docker images on a good day for us.
Besides we don't always blow away a VM for all services (ie the ones that don't need a cluster of nodes). We reuse them (yes this is eschewed but we get super fast deploys). I suppose this could be said for docker as well though.
Also with Docker our build artifacts would be much bigger since instead of a executable Jar we would have images. The IO of transferring images from the CI server can shockingly take some time.
Sure, you can create a blank, empty VM in less than five minutes... but the point of creating a Docker image is that it has everything pre-installed, ready-to-go.... you're not even remotely comparing apples-to-apples.
Large images aren't an issue anyway, since the base layers will just be cached...
I said I'm comparing with what I know and experienced (and this is for a JVM shop). I'm sure we could have gotten Docker to probably to be faster especially given your passionate comments (and it appears after googling there have been improvements in docker build time).
But I just ran gcloud to create a VM with Java and copied a Jar in under a minute. I just can't figure out a way to get docker to that speed. Are you creating images and copying that fast? We must me do something massively wrong with docker.
EDIT:
I found out the reason... It appears we had some issues with the Docker cache and had to disable it (I don't know the exact details why yet). Please disregard my comments on slow docker building. Apologies. I wish I could delete my comments and feel a little bad about potentially spreading incorrect information...
