They prescribe it because their therapeutic text books still say to use it, and are not updated. It is a sad fact, but along with the B12...doctors will test, and then either not apply the correct therapy or ignore the results.

Here is the study that showed D2 is far less effective than the active D3.

The original D that was RX on the market (now generic) is over 40yrs old. Back then that is all there was. It was made by Lilly and called Deltalin, and was sold to another company who renamed it Drisdol.

This explains it in more detail.
http://articles.mercola.com/sites/ar...d-mistake.aspx

Doctors in general know little about nutrition, supplements, testing and one has to expect to do their own work in this area.
Integrative doctors, may be better, but they are new, and we don't see many posters going to them. In fact we only have one poster posting about that, currently. They are just beginning to show up in searches on the net.