Except lower fares wouldn't increase ridership anywhere near enough to make up the difference, and would surely produce a loss of revenue.  That's because BY FAR the biggest reason a person doesn't use rail is because it just doesn't fit for where they need to get to/from and handle what they need to handle.  

It's already a hugely subsidized bargain compared to owning/operating a car and driving.  Most of the people that rail is a good fit for are ALREADY using it.  Heck, they could double the fares and most of those people would STILL use it because it would STILL be a bargain compared to owning a car and driving.