The current image ships Node.js as well as yarn, npm, bash and a lot of other binaries. It's also based on Ubuntu. So you have a fully fledged operating system with all its little binaries and utilities.
You don't need any of those when you run your container. The only dependency you need is Node.js.
Docker containers should wrap a single process and contain the bare minimal to run it. You don't need an operating system.
In fact, you could remove everything but Node.js.