My understanding was that the sentences were too harsh and they were scared everyone would flip.

Obviously there has been ancillary involvement with drug dealing on a individual and crew basis, but I think the anecdotal evidence suggests that they never went all in or anything close to it. I would imagine that drug trafficking from the time it really became a thing in the 60s/70s was by and large too hot. If you become a major player you are eventually going to get caught.

It is probably the most lucrative of all criminal enterprises and as many doofuses as there are/were in the mafia, they are practically geniuses and organized better than GM compared to most criminal enterprises. If they'd wanted to get in, they had the infrastructure and aptitude to dominate the entire thing, like they did alcohol.

They didn't; to me this suggests there must have been some kind of quasi uniform decision at a high level.

Just my opinion.