And in some cases it really doesn't make that much sense. I think there is definitely some urban vanity at play with the huge investment in train spending. Would personally love to see more bus rapid transit lines.
Commuter from Seattle here. BRT is an improvement here (I'm on it now) but vastly inferior to rail. Downtown to UW is 10 minutes on rail. My similar distanced BRT commute is 25-60 minutes.
Grade separated rail makes a gigantic difference and moves leagues more humans faster than BRT could dream of.
Unless BRT gets dedicated lanes it's no better than any other bus, except it stops is fewer places more often.
I thought, and wikipedia agrees, that BRT implies dedicated lanes, for at least the majority of the route.
There's lots of little improvements that could be made to bus transport, for similar money to trains, I think a big part of it is just wanting to be responsible for big construction, whether to get kickbacks or to just a more straightforward ego boost.
Here's a peak at what Metro might be up to the next 40 years: http://la.curbed.com/2016/3/18/11265444/metro-los-angeles-ba...