Good sensors aren't cheap, the optical and mechanical elements aren't likely to drop in price soon. Only the computing power is getting cheaper, but harnessing it isn't particularly easy (we're not getting better at programming as quickly as we're making faster chips).

If you need another example, consider automated cleaning robots. It's a considerably simpler problem to solve, and they're still only a marginal product. At the moment, autonomous tech is only really used in well-controlled industrial environments. It will surely break out of there progressively, but chances are it will take a while.