This is not my area of expertise, but from a layperson, my understanding is that when you are applying for a drug approval status and you have to go through human clinical trials, you have to do that with each individual active ingredient in the medicine you're looking to get approval for. Cannabis has over 80 active cannabinoids. Then there is a whole other class of active ingredients called terpenoids, or terpenes, which are responsible for the flavour and the smell that distinguish the strains. Emerging evidence is showing us that the terpenes also interact with our endocannabinoid system and have therapeutic effects.
My understanding is that cannabis is a very complex plant and doesn't fit easily into the pathway in the way that we regulate pharmaceutical medicines, which are often single active ingredients. It's a plant that has many different active ingredients. Again, it's not my area of expertise, but I also understand that you have to go through clinical trials for each one of the indications that you're seeking approval for, and cannabis is used for an incredibly wide range of symptoms.