The decline of alcohol in the services predates even serious consideration of integrating the services. A combination of factors have changed matters, but the two biggest are:
-Alcohol has always been trouble for discipline and getting work done. It was just... unavoidable. People didn't drink water, they drank weak (or strong) booze, and that shaped cultures. It was still trouble, "What do you do with a drunken sailor?"
-Other drugs came to dominate, either openly or prescribed (Go and No-Go pills for example) or covertly and for fun.
http://theconversation.com/the-enemy-within-the-battle-over-...
https://www.ncbi.nlm.nih.gov/books/NBK207276/