Great question 1956.
Our bodies are all different.
Sometimes an unknown cause of osteoporosis is operative. If you have parathyroid disease your body might produce too much parathyroid hormone. If you take a drug like (my favorite) Forteo, which works by increasing parathroid hormone, you already have too much and you'll probably get sick.

But I should have started at the beginning. Twenty years ago there were no anabolics--no drugs that actually build bones. All we had were the bisphosphonates (well, and salmon calcitonin which doesn't work). Bisphosphonates don't let your bones remodel. Normal processes of repair are stopped. Bone builds by holding older bone in place. The cracks that normally develop still developed. So you have this bone that is only stronger than no bone. But that is all you have to prevent fracture. And bisphosphonates prevented more fractures than they caused.

In 2002 Forteo was approved by the FDA. It had a black box warning about the possibility that it could cause bone cancer. Mandated after market studies completed just this year removed that concern (and the black box). Tymlos followed Forteo with the same warning also removed.
Prolia was next and widely hailed. Years have proven that it can be a dangerous bone breaking drug if not followed by other drugs.

2019 Evenity. The hazard warning with Evenity is cardiac. Some dismiss the warning and prescribe the drug In the years ahead, patient health will inform us whether the drug is too dangerous to take or as safe as Forteo.

Prescribers are largely influenced by what has happened in their practices. If they have a patient who was harmed by Prolia, they won't prescribe Prolia. And, they are more reluctant to trust Evenity.
Sometimes cost and insurance coverage controls the prescription.
Interesting question, complicated answer.