Ask HN: Who is paying for servers/bandwidth used to build Docker images

Just wondering with containers being on the rise as well as continuous testing/integration apps such as CircleCi, Jenkins, GitHub Actions,...

When someone uses apt install curl to build a Docker image, curl package must be hosted somewhere by an organization which is paying for the storage and bandwidth. Do these organizations rely only on donations?

Many new developers won't take advantage of Docker cached layers and reinstall over and over again linux dependencies, composer packages, ruby gems etc...

The real question is how can it be sustainable in the future as we are going to have more and more developers and more and more container images to build?