Because local postgres is a bad time unlesss it's the only thing running on the server. Even then sqlite will smoke postgres (even with unix sockets).

The point is to survive the Pareto row locking problem you need to move away from a network database (if you want to still have interactive transactions). The network part is the main point of a network database, once you drop that there's not much pointing sticking with the added complexity unless there's another feature you really need.