This assumes money is the only factor and motivation.
Only if you assert that it is only useful if it solves 100% of the cases.
There are other motivations, but money is a big one. If you could block X% for a large value of X (I'd say easily > 50) then you're better off than before, even if some insiders driven by other motivations still remain.
Still your point stands that money is a common factor. However you still have the problem that bribes usually aren't a one time payment but an ongoing thing, so a purely financially motivated adversary would take the total value into account.