Small space debris is a serious problem. I think that if a large container orbits full of space debris and sweeps up small pieces of space debris that fit into the container, the space debris can be cleaned up cleanly. Why is this method not used in practice? In what ways is it limited and in what ways is it inefficient?
The problem is that every bit of space debris is in its own orbit. If you want to match that orbit, it takes a lot of fuel. If you don't do that, and you just intercept it, you will find that the debris is flying at a high speed (several km/s) compared to you. This means the debris will punch a hole through your container, like a bullet, instead of being caught.
From a diplomatic perspective: you say space debris cleanup, I hear anti-satellite weapon.
If you announce you have the capability to do this, you are going to attract the attention of all the major spacefaring powers, who have invested heavily in their satellites and rely on them for both civilian and military purposes. If you are one of them, you risk starting an arms race and accelerating the militarisation of space.