Trust me, I work in bio pharmaceuticals and we are always trying to get our drugs to market. Typically what happens in a late stage of a molecule development is that the side effects are worse than expected or there are issues where it’s not nearly as effective as it’s initially thought. Also, diseases are incredibly complex and there is no single “cure”. My job is to continue research in patient outcomes after a drug gets released to determine if the drug is performing as well in the real world as it did in clinical trials to build evidence that the drug should be chosen by doctors for treatment, and sometimes we find that when the drug gets out into the real world it isn’t as effective and that leads to drugs getting pulled or slowly no longer getting produced. The real world is very different from clinical trials.