Because most selfhosters are too lazy or inexperienced to break away from cloud services. Docker is great but it has also enables a “just run this docker” mentality that mirrors the Windows “just run this exe.”
edit: I think that the opportunity to learn how a project works, how to debug problems and how to integrate a project into their own setup is obscured.
“File Browser” or “Sharry” allow you to make public links to share files with others BUT you need to run them on a server that is accessible to both parties.