This matter has been widely discussed here by people much more knowledgeable than me, but I’d say it boils down to two major factors: 1) three murderous power struggles that triggered plenty of trials and made many guys flip; 2) sort of nepotism by the Persico clan.

also some have said they've always been more involved in blue collar crimes than high income schemes.

this said, if my memory doesn’t fool me, the recent Amato bust was the first one in a while. Some sources said they’ve made quite a few guys and rebuilt decently in recent years.