I was amazed anyone tried to make a free Docker registry. It's like making a CDN, except instead of individual files, it's for a whole app and all of its dependencies. It's a crazy amount of data for storage and bandwidth.
It's more akin to making and then running a CDN but only charging 10% of customers. I'm sure Docker the company was writing it off as a marketing expense, but if they were running this in one of the public clouds that charge for egress, they were paying out a boatload of money just in egress charges (plus more in storage costs)
Well of course you've got to do that in the first place to get people to sign up to the docker model and become dependent on registries in the first place.
Yeah. What if someone had said "Wait, is this sustainable?" before building up a docker-based solution that. (I wonder if we can find any archived discussions wondering that, or if we're just so used to thinking "things can scale for free indefinitely on the internet" that nobody wondered?)
Now that they have it, the cost they are willing to pay is based in part on cost-of-switching. Which is pretty enormous, directly and indirectly, when entire ecosystems based on docker have been iterated.