I think it's the demand thing myself. Serious students usually have a particular motivation e.g. living and working in Russia, job-related needs. Hobby language learners IMHO are more likely to opt for something easier to learn (they want to spend some free time learning a language, not sacrifice their whole life for it!) and something they can use on the usual holiday destinations. I don't know a lot of folk who go to Russia for their holidays.

I would love to have a hundred Russian language exchange contacts, but right now I don't even have time for one.