What's happening is further research on the medicines are being done which show medicinal benefits for off label use. In many cases, it's researchers seeing a drug has a known side effect and saying "Hmm, I wonder if that side effect can counter this symptom".
What's lacking is the final FDA approval for the drugs being used for these off label treatments. That's because these drugs have to go through all the same tests that are required to get FDA approval in the first place.
IMO, for already approved drugs there should be a faster secondary route to getting these drugs approved for current off label usages. Ideally, it'd be something the FDA itself spearheads in partnership with the likes of the NIH.
Problem with doctors preascribing against FDA is that it can lead to problems or abuse.
Om an unrelated note, FDA could have been bribed to ban something same way a doctor cpuld have been bribed to prescribe it.