There are a number of possibilities. It could be that, like your rheum, they don't think (from their schooling and experience) that it's likely that you're deficient. Many doctors believe (probably because they're taught) that we do get most all the vitamins we need in our diets, so in the absence of any obvious observable symptoms, they won't test.

It could also be an insurance issue. A doctor may be willing to order a test, but is reluctant if s/he knows it will get bounced back by insurance companies (who don't think it's necessary).

It could be their minds are on something else. Doctors (on average) only hear about 25% of what their patients tell them, and patients (again, on average) only hear about 50% of what their doctors say. That's what they tell me, anyway...

You might try just asking them. My PCP is kind of ambivalent on testing; while he doesn't believe in doing much of it himself (with a few exceptions), he's stated many times that if I want a particular test, he'll be happy to write up the order.

Doc