A bunch of people have written about this. One major obstacle is that it's difficult under the law to get the Sacklers themselves convicted for actions taken random executives in the corporation, especially if (as has been written) the Sacklers were not themselves intimately involved in the operations of Purdue, but rather just the beneficiaries.
I'm not here to defend the Sacklers, who are odious. I'm just saying that there are reasons they aren't on trial for their lives, but rather having their assets attacked.
(I have no opinions about the immunity from further suit they've apparently obtained.)