afaik, canonical does build those images. See here: https://cloud-images.ubuntu.com
In any case, what I'm asking for is some conversation between Canonical and Docker, Amazon, etc. To see if there's something obvious either side can do to skinny these down. The ubuntu image is for sure the most popular AMI, and I imagine one of the most popular docker ones. The collective bandwidth and time gain of optimizing the size would be significant. Currently, the ubuntu images are significantly larger than other popular images.
That said, what's "minimal" to one is not "minimal" to another. We can certainly take stuff away, until you end up at Alpine or Busybox size. But then we've stripped away the essence of what's Ubuntu. So it's a very delicate dance!