Hmmm wouldn't say they necessarily "fell off". The same thing happened to the Outfit that happened to every other American Mafia family. There aren't as many Italians in Chicago & Philadelphia as there are in NY, so the numbers will naturally make it look like Chicago & Philly have been hit harder, but the Italian American population, not to mention culture, has assimilated itself within those cities & is shrinking rapidly (has been for a long time). Italian American organized crime will naturally follow suit.
The idea that the Outfit is this gasping typewriter factory that is barely keeping it's head above water, and which consists of a few old bastards making the poker machine rounds, is laughable though. The Outfit is an institution & still a viable, feared criminal entity. Not what it used to be but still in place, and still keeping youngsters in the ranks.
Philly was nothing compared to Chicago. They were a national powerhouse up to the 1980's and basically ran the show west of the Mississippi. Now they are struggling to hold on to the Chicago area alone.
And Chicago was nothing compared to the 5 families.
Maybe Chicago was top of the second tier above Philly...but they were never in the top tier with the 5 families in NYC.
It seems like you are putting them in that category in their prime, which I disagree with.
In fact, in their prime, I would say Detroit gives Chi town a run for their money.
But Chicago, Philly, Detroit, were NEVER in the first tier of families...IF that is what you were implying.
