Why remove the vegetables from vegetable stock?
The point of stock is to extract the maximum flavor from whatever you are using, be it bones or vegetables. Once extracted there's not a whole left, which is why you don't boil stock bones over and over. Vegetables will not have much left to give after being used for stock, you can still eat them but they may not be flavorful or nutritious.
Unless you're making a stew you're going to be cooking the stock, then removing the vegetables, then cooking the stock more with other ingredients. If you leave the vegetables in they'll continue to cook until they break down, and that's usually undesirable.
If you are making a dish where you want to eat the vegetables with it then you would either want to extract them while they still have some texture and then add them back in at the end to re-heat, or add them towards the end and cook them till done.