"I don't see why a doctor just can't write a prescription."
Because it's not an FDA approved medication for any medical use.
"#1 because, according to the gov't classification of drugs, MJ has exactly zero medical utility."
My understanding was that no company has gone through the process of doing the necessary studies to test it for medical use, and therefore it's classified as controlled with no medical use. Companies would not be able to sell it with patent protection since they didn't invent it, so there is little financial incentive to go through the process.