Trains are expensive upfront, which might favor buses when expanding into new areas. But if the infrastructure is already there, a train line will always be more economical in the long run than the equivalent bus line.
So ripping out existing serviceable train tracks is stupid (or alternatively: evil) if you think in the long term.
As I said in another post, train tracks don't last forever and are expensive to replace. And trains really only benefit from dedicated ROW, a streetcar is worse than a bus in many respects. (Except appeal.) People back in the 1950s were not stupid or evil, they made a decision which made a lot of sense at the time.
So ripping out existing serviceable train tracks is stupid (or alternatively: evil) if you think in the long term.