An Interesting Analogy explaining Node and NPM

I had difficulty in understanding why a package manager is used at the first place. Why can't we just embed them into the runtime environment?

We know that Node.js is a JavaScript runtime environment helping to execute it outside browser. When we install Node, Node Package Manager (NPM) comes preinstalled with it. The purpose of npm is to:
A. Serve as an online repository for sharing open source JavaScript packages.
B. Providing a CLI to interface with those pckages.

My question was -- If npm is preinstalled with Node, doesn't Node also carry all the packages? It contradicts the basic use of a package manager to avoid installing all available packages. But there was a major flaw in my doubt, and yeah of course I am a beginner so don't judge me.

Notice how I said "an online repository". Let's understand this with an analogy I came across.

Think of Node.js as your house, npm as a delivery driver, and the npm registry as a massive online warehouse (Amazon).
When you install Node.js, the delivery driver (npm) moves into your house.
The driver arrives empty-handed. They do not bring the entire warehouse with them.
Your house stays small and clean because the millions of items in the warehouse are still sitting on shelves thousands of miles away.

npm gives you the flexibility and freedom to choose what you need according to what your project demands. Separating package managers like npm from the runtime environment (like Node.js) is a deliberate design choice that prevents software development from becoming rigid, bloated, and insecure.