As mom2rtk said, DLR stopped accepting WDW tickets just after WDW switched over to the RFID tickets (in late 2013). Prior to that, they would allow guest to use WDW tickets to enter DLR (exchanging one day at a time), but it was never a written/official policy. After WDW switched over to the RFID system it became more difficult for DLR to figure out if the tickets were still valid and if so, how many days they had on them (WDW and DLR uses two different ticketing systems). My guess is that it just proved to be too cumbersome, so they decided to stop doing the exchange, but because it was never an official policy, they didn't have to make any sort of announcement.