One important aspect concerning alternate airports Minsk and Vitebsk is that both of them are not in Russia, but in Belarus, and president Kachinsky was never a friend of president Lukashenko (neither are other European presidents). So diverting there could never be a good political decision. As seen from the transcript, Smolensk ATCs didn't expect the plane to divert there, they offered one of Moscow airports in their conversations. And as far as Vitebsk airport was closed that day, it seems that the Polish side really never expected that the flight could be diverted there, they were in the flight plan just because something had to be there...