This is just a part of XaaS infrastructure and XaaS is widely used. Git hosting (e.g. GitHub), file hosting (e.g. S3), VM or container "hosting" (e.g. Heroku), mails... Why can't Docker images couldn't be hosted in the cloud ?
There are still a whole bunch of companies who aren't on the bandwagon of putting their code up on the Internet. In fact, there are a whole bunch of companies who likely cannot due this due to various regulations and contracts with their clients.
I'd also add that closed and open source often feed into each other in a kind of symbiotic relationship. Sounds controversial to the libertarians and hard-core open source folks but that's the way it usually plays out.