The users that don't care are almost always the users buying the smallest (personal) amounts, and they usually don't care because they know if they get scammed or it gets lost they only lost $30. The customers who want larger quantities very much do care, and they're the ones who spend real cash.

Furthermore it's pretty common for a dealer who has a good enough reputation to start requiring early finalization. Most of the reason people still used SR2 is it was the easiest place to find their favorite vendor, and the lack of escrow didn't matter because you trust him and/or he requires FE no matter what the market.

As for why people will use OB (I have no idea if they will), cops aren't the only thing to worry about when buying drugs on the darknet (in fact they're close to the bottom of the list). Several marketplaces (including SR2) have been hacked and had all the users money stolen, and a couple have just disappeared with everyone's money. I suspect the selling point will be more like: "Hackers and corrupt admins won't be able to steal your money! Plus it's never down! Plus it's harder to get arrested!".