Hmm...This paper explains the "why" in more depth, and digs deeper into the importance of customization.

From https://pmc.ncbi.nlm.nih.gov/articles/PMC7963175/: "The recommendation for a drug holiday up to three years is derived primarily from extensions of pivotal trials with alendronate and zoledronate and select surrogate marker studies. However, certain factors may modify the duration of bisphosphonate effects on a drug holiday and warrant consideration when determining an appropriate time off-therapy. In this narrative review, we recall what is currently known about drug holidays and discuss what we believe to be the primary considerations and areas for future research regarding drug holiday duration: total bisphosphonate exposure, type of bisphosphonate used, bone mineral density and falls risk, and patient sex and body weight....

Changes in risk factors for fracture are perhaps the most important consideration when re-assessing appropriateness of a continued drug holiday. Risk factors increase the probability of fracture without osteoporosis therapy, and the risk-benefit ratio of a drug holiday diminishes...[H]ere we focus on factors that are most likely to change during a drug holiday. These time-varying risk factors include bone mineral density (including initiation of medications that may lower BMD) and fall risk (including initiation of medications that may increase fall risk)....

Thus, even with all other fracture risk and prior therapy factors being equal (i.e., treatment is indicated and the patient has low BMD), people with larger body frames may not derive the same lasting anti-fracture effects during a drug holiday as those with smaller frames due to less remaining bisphosphonate in proportion to bone size...

All other factors considered, based on the current evidence, a longer drug holiday may be more appropriate for patients of Asian ethnicity versus Caucasian or Black patients, due to lower major osteoporotic fracture risk and higher risk of adverse events from long-term bisphosphonate therapy...

To date, little data examine the effects of osteoporosis therapy effects in men, let alone the effects of drug holidays."