If the waste was to be shipped to Mayak, future maintenance or the lack thereof would be Russia's problem alone. The U.S. military, which is in charge of the Cooperative Threat Reduction program, appears to be in favor of waste transportation to Mayak. But that does not necessarily reflect the CTR program office's preferred solution. As a consequence, CTR is careful not to alert congressional foes of the program to any activities they could use as ammunition. Ultimately, the discussion burns down to the question whether it is possible to prevent Russia from reprocessing nuclear materials in case they are shipped to Mayak.
DoE hopes for an agreement prohibiting reprocessing.
It may make sense for the European side, and particularly for Norway, to have the nuclear waste stored as far away from its borders as possible. But agreements are rarely signed because they are beneficial for one party.