Contracts generally need an end. You can’t have a “this is how it will be forever” (in perpetuity) in there, without someone saying that it isn’t legal. So if you want a long contract, but need it to technically end, people came up with the idea of basically saying “as long as anyone currently alive is living (plus some time)” but that isn’t practical and reasonable to test… so who is a high profile person that will live a long time? Members of the Royal Family! This survives today in American contracts (long after our British colonial days) and recently showed up in a well covered Disney contract.