Several things. Mostly that it has to be rolled out slowly because people lives are at stake so testing can run for quite a bit longer than you’d expect. Also that everyone wants to be the one who makes the breakthrough so companies will claim its right around the corner (like fusion) repetitively, i.e. Tesla saying it’d be here in 2018. We’re just at a point where these things can use parking lots so I wouldn’t expect a complete rollout several years as systems are built on top of other systems that have been widely tested and confirmed to work.
