For the most part I think most of these tracks that going under are old. Built too close to a rapidly growing human population. The real estate, at some point, becomes so valuable to these owners that they would be absolutely STUPID not to sell it.
i have always been under the impression the build up around existing tracks is the root cause of tracks closing, even if those tracks are old. too many people encroaching on proven establishments with greed being their main concern in life, and to hell with the integrity of those that were there first !
