Is there some legalistic reason companies don't seem to keep a funnel of quality CVs for candidates and reach out to them when a role looks like it's going to become active?

This whole "application," process seems like the artifact of a kind of historical paternalism among employers that doesn't reflect reality anymore, and it seems to be an unneceessarily synchronous bottleneck in the talent market, where both parties (employer and employee) have to time the market correctly. Objectively, that seems...limited.