Yes, everyone overlooks this and talks about how Docker containers are "app-only images" or something. They're not app-only. They may be using a thin OS like Alpine, but there's still a completely independent userspace layer. The only thing imported from the host is the kernel. If you made VM images in the same way, they'd also be 200M.

The benefit of "containers" is that you don't need to siphon off a dedicated section of RAM to the application.