What happens to trains after they are too old

It seems to me that much of the pre-revolution old style Trackmaster stock that was pulled from the shelves, along with unshipped warehoused stock, seconds, and parts, were sold back to China and is what is flooding the market by the dozen or so new Chinese sellers on eBay!?!?
Also many stores like Target, Kmart, Walmart, and ToysRus, kept their remaining stock and still sell it on their online sites.