How often does the US experience medication shortages?

My sister was just informed that there is a Lupron shortage, so they might not have it for her next month. I looked it up, and it appears to be a legit problem nationwide. Wtf?

How does such a thing happen? Would there have been a drastic increase in cancer, resulting in a spike in demand? Or is the company just not making enough?

I understand that getting healthcare is difficult in the US due to lack of health insurance and extreme costs. But this is a whole other level of shit that I didn’t know existed.