Because it's an application platform, you make apps with it in Lua. I think there's even a full framework for it now.
Docker is more than just application containerization, it also lets you infra as code to some degree. You can specify where and how files are organised. It turns a git repo into something consistently runnable with the same commands as every other repo you may maintain.
There's value in that.
This is just gatekeeping.
But the irony of the situation is still there.