It's hard to call it "abuse" when Docker has been allowing -- and IMO tacitly encouraging -- this usage pattern for most/all of their existence.

I get that bandwidth is expensive, but this feels a bit like the usual "make it free to get lots of users, and then start charging when everyone is locked in" plan.

If they really just want to reduce their own costs, they should be evangelizing the use of a caching proxy, and providing a super easy way for people to set one up, both on the server and client side. (Maybe they already do this; I haven't looked.)