Gas and coal are cheap and the waste from burning them can be dumped into the atmosphere and nobody cares enough to stop burning them since that would increase the price of electricity and cost jobs (see "War on Coal"). Nuclear reactors, including breeders are expensive to build and everyone is petrified of spent fuel from reactors because they've been fed bullshit and crappy movies about the effects of radiation ever since 1945.
Using up spent fuel in new-design reactors by reprocessing and other means will cost money and new uranium fuel is really cheap at the moment (current spot price for U3O8 yellowcake is $34.15 per lb) and it will remain cheap for another 50 years and more as more mining sources are developed and brought into production.
The Russian BN-800 reactor is designed to burn spent fuel and also plutonium from decommissioned nuclear weapons but it's quite experimental and it will be a while before more reactors like it are built. The fuel for it still needs to be processed and specially fabricated, it can't just take used fuel pellets and this adds to the expected cost of operations.
Some countries such as Russia do reprocess spent fuel but that only concentrates the unusable isotopes that are actually waste and they still need to be dealt with, probably by deep geological burial. There doesn't seem to be any real problem with this idea but it gets a lot of attention from the panic merchants with the 100,000 year figure being thrown about a lot although that's quite arbitrary considering the environmental radiation sources already present around us naturally which do not emanate from the nuclear power industry.