Sales potential of the MiG-31 series?

Okay we always hear mention about Sukhois and sometimes MiG-29 on the market but what about the MiG-31s? Why hasn’t it been successful on the international market (that is if it’s offered)..

Off the top of my head, I think only Russia and Kazakhstan are active opreators of the type..

so what are the possible reasons of it not being sold so well and what types of customers can it attract?

off the top of my head..

cons

1. perhaps the unit is too costly? after all most large aircraft are costly to maintain

2. limited role in just air to air? but then there are new variants that seem to expand that ability

pros

1. supposedly the Zaslon-M is the most advanced Russian radar out there

2. seems like it has good endurance and combat radius

3. the R-37, if it is a much improved version of the AMOS would seem to be a decent long range AAM..