the reason is that there are no profit for pharmaceuticals to pursue this
But, as others have said, this just isn’t true. Obviously there’s no profit in (say) proving that brewing up a cup of tea using common plant X cures illness Y. However, the picture is more likely to be that plant X shows signs of pharmacological properties, but the trad method of using it gives a dose so variable that it’s an unreliable treatment. If there’s a bad need for cures for illness Y, then there’s definitely mileage in research to develop mass-market forms with standard dosages. Case in point: artemisinin again.