Aside from the incentive to just pretend that it is somebody else’s problem; the oceans have the tricky complication of having a great deal of desirable life mixed in with the trash.
If you just want to remove all the solid objects from a volume of water; anyone involved in net-based fishing could help you out(though you might need a net fine enough that nobody would admit to owning one on the record); but you would probably be unhappy about the ratio of recovered plastic to dead fish. In space, there’s mostly nothing; a comparatively modest number of satellites people care about in known locations; but not many endangered celestial cod to worry about(and the magnetosphere discourages solar anchovies).
