There is actually a substantial amount of flavor left, but just like in coffee, it's very difficult to extract without increasing the surface area of the vegetables and meat you add in. And how can you increase the surface area? Exactly the way you'd expect to.
Yeah I blend my ingredients sometimes. It produces a very intense stock which is not always what I want, but it is quite good. Recently I tried blending and then browning the blended result. It worked decently well.
James Hoffmann has a video on this topic https://www.youtube.com/watch?v=VV68NiRulEk