Talent poaching at upper levels

I'm guessing there's quite a lot of poaching going on at senior levels in IB and across other industries. But why isn't there more poaching going on? Is it because there's an equilibrium point where giving a higher paycheck just doesn't make sense for the poaching firm? Or is it loyalty to company/wanting to build up a particular team/company that prevents senior managers from wanting to leave? Or perhaps poaching works better in theory than in practice, eg. you can put together all the best players in the league to form a dreamteam but they simply don't play well together? Some combination of the above?