I can't speak to the specifics of your questions but I think it's more of a post 9/11 thing than a Bloomberg thing per se. There's a lot of positive things to be said of Rudy and now Mayor Mike, but neither of them are any different than their Democrat predecessors when it come to knife-as-tool, much less knife-as-self-defense, type of thinking.
There's another factor, too: real estate prices have been insane in the city for quite a while now, and I am guessing that if a trad army-navy store loses its lease, it can't live with the increases that the location can probably demand now, so they go out of business. This has been going on for a while, and frankly many of the army navy type stores were only selling knock offs any way.