The biggest reason is social, or occasionally legal. There are tons of barriers in place to getting the legal system to agree that smart contracts are legitimat

The biggest reason is social, or occasionally legal. There are tons of barriers in place to getting the legal system to agree that smart contracts are legitimate - which creates a barrier to real world, because regulators of real world business want to see contracts and legal language. (And you can't get away from if if you're operating a physical store with physical employees) The only group that has managed to beat this was early Uber, and their political lobbying arm was legendary.