We don't have Scheme in our entire country (here in India) but that honour goes to C programming language.
For the purpose of my answer, substituting C for Scheme, I keep asking myself, why bother with C. After that 1 semester of C, I have never used C professionally anywhere. In fact, once I step out of educational purposes, C becomes useless. That begs the question, after almost 25 years, why are they still teaching C? Why not something else?
I think, why they are still teaching C (in my country) and Scheme (in yours) is probably because it is ubiquitous. there are any number of books written on C. More importantly, the faculties who teach them ( I think most faculties change their jobs once in 60 years) can teach the same thing for the rest of their lives, use the same lab manual, and use the same code, and ask the same questions, use the same evaluations. From a strictly logistical point of view, it makes sense to teach C 30 years ago, and 30 years hence.
Can you image the mess, if every five years, the universities change their syllabus? Thats a logistical nightmare (not to forget other challenges) no one wants to deal with. For instance, one university could decide to go with C sharp, and another with Java. That creates all kind of problems. However, if all universities agree (which is how things are now) to simply keep using Scheme (in your case) and C (in my case), life becomes simple.
Further, the foundation that you get by learning an ancient language is that, everything that came after it, be default, would be easier. I learnt to ride a bike (as in motorcycle, not bicycle) in my dads old bike which was, well not that good. However, because I drove the tough one, all of today's bikes seem like child's play. Although I don't use C itself, anytime I learn a new language, I unconsciously compare it to C, and learn from that.
Update 1 : To add some context, I have been part of the IT industry for 11 years, and 5 of them as a developer/trainer/educator who travels widely. I am sure C is used somewhere, I haven't seen one single enterprise usage of C and I have worked for startups, small companies (less than 100 employees) and for MNCs (more than 2000 employees) and never ever has any division, anywhere talked about C, used C or implemented C.
Again, no disrespect to C (or its legion of fans) but I request that my opinion be taken in this context.