Yes, but speedway in Russia is popular in a limited number of places, as indeed it is in the major speedway nations as well. I'd certainly put Russia high up in the second tier of speedway nations, but population and geographical size isn't really much of a qualification for staging a GP somewhere.
It makes no difference to them at all. The local promoter, except where IMG/BSI promote the event themselves, assumes financial responsibility for a GP. IMG/BSI get the same sponsorship and television money regardless of how many fans turn up.
Yes, but how much is each fan paying? It's all very well getting 15,000 fans, but if they're only paying the equivalent of 1 pound each, then overall revenue is still the same as 1,000 fans paying 15 pounds each.
The physical ability of Russia to stage big sporting events is not really in question. It's the financial and logistical arrangements that are much more complicated than if you stage events in an EU country, as anyone who has ever done such a thing knows. For starters, unlike Latvia and Slovenia, everyone travelling to Russia needs a visa, then you have to make 'arrangements' to ensure your equipment isn't indeterminably held up at customs until after the event. And so it goes on...