As someone preparing to lay down a small (1/5 scale) railroad - you vastly underestimate the expense, difficulty, and maintenance requirement of rail. Switches and diamonds (intersections) are especially troubleprone. 2% is considered a serious grade. And derailments happen, more frequently with higher speeds and deferred maintenance.
If our rail network was as potholed and badly maintained as our roads, people would die in train accidents every day.
Rails are great for intensive, carefully manicured routes. They are not a substitute for roads.
There seem to be fairly regular (at least, more regular than one would like) AmTrak derailings in the US. That isn't to say I think it is AmTrak's doing specifically, I think it is like you said a maintenance issue coupled with everybody else who isn't on the train interacting with it.
Then there are the cases of engineers who are distracted and what not, but I'd imagine we're talking autonomous so that (hopefully) wouldn't be an issue.
If our rail network was as potholed and badly maintained as our roads, people would die in train accidents every day.
Rails are great for intensive, carefully manicured routes. They are not a substitute for roads.