1. Reviving a "railbanked" right of way is frequently not as easy as it sounds, particularly if it has been turned into a bike trail or walking trail or some sort of linear park. All the anti's come out of the woodwork to oppose it for all sorts of reasons, real and imaginary.
2. Many railroad right of ways are not absolutely owned by the railroad, but are on easements that revert to previous landowners once the track is taken up. One example, in Dallas DART, DART had to defined as a railroad by the state legislature so a section of one of their lines could be transferred directly from railroad to DART rather than DART having to chase down all the descendants or buyers of the original pre-railroad land. Without something like this, the right of way simply disappears when the track is removed.
As an aside here, when buying or selling a piece of land that is in part used by some form or road or utility, (a lot of rural roads are on easements, not absolute right of ways) make sure the transaction does not exclude the occupied area but does acknowledge it being "subject to" or whatever the appropriate legal terminology is in order to avoid headaches later on.