Why remove the vegetables from vegetable stock?

It's likely the concept of "mushy vegetables" that throw people off. The texture of overcooked vegetables isn't the best, and the vegetables will eventually lose their vibrant colors and become grayish/brownish.

As you continue to cook the vegetables, they will start to break down, and un-sightly bits will start to float around in the stock. All those factors may contribute to the filtering out step in the recipes, but at my household, that would be too wasteful.

I'm specifically thinking of ways to try and add flavour to the broth of vegan noodle dishes...

If you don't already, I highly recommending you try using dried medicinal ingredients, such as shiitake mushrooms and whole peppercorns; we use them (as well as some other ones) every time we make stock.

Why remove the vegetables from vegetable stock?

It's likely the concept of "mushy vegetables" that throw people off. The texture of overcooked vegetables isn't the best, and the vegetables will eventually lose their vibrant colors and become grayish/brownish.

As you continue to cook the vegetables, they will start to break down, and un-sightly bits will start to float around in the stock. All those factors may contribute to the filtering out step in the recipes, but at my household, that would be too wasteful.

I'm specifically thinking of ways to try and add flavour to the broth of vegan noodle dishes...

If you don't already, I highly recommending you try using dried aromatic ingredients, such as shiitake mushrooms and whole peppercorns; we use them (as well as some other ones) every time we make stock.