There are some other considerations for polar route flying. One is radiation exposure. With less ozone over the polar areas the exposure is higher. Also another biggie is fuel temperature. If it's really cold for an extended period and Jet A nears its minimum temp it can get waxy and then bad things start to happen quickly. For 121 ops some other considerations are spotty weather reporting and few diversion options in Russia. Along with that, if a large aircraft did divert, there's not a lot of infrastructure to support a planeful of passengers at most of the divert locations.