HOW LONG MUST I TAKE BISPHOSPHONATES, OR?

This week, a tweet led me to a brief item from Mayo Clinic: 

Mayo Clinic

"Most people don't receive any additional fracture-prevention benefit after they have been taking intravenous bisphosphonates for more than three years or oral bisphosphonates for more than five years."

The item went on to indicate that we might want to stop bisphosphanates at that point, but with a qualifier that later, if our bones scanned as fragile, our physician might restart the medicine then.

For some reason, that item suddenly pulled me back to a study I saved a few years ago when I briefly considered bisphosphonates.  (For several reasons, I can't take them.)   

Before I went on to Prolia, I had accumulated a big file on bisphosphonates, and the following was in red in my BONES file: It's got good news and for some, bad news:

NEJM Catlyst:

Consequences of poor compliance with bisphosphonates.

BA¹, Andrade SE, Yood RA, Kahler KH.:  

Conclusions:

" Reductions in fracture risk and overall health costs can be detected in individuals achieving as little as 60% to 40% compliance with bisphosphonates. However, as many as 34% of patients in the first year of therapy and 52% by the third year will not reach even the minimal compliance levels required to receive benefits."
Published by Elsevier Inc.

So apparently, it's not just for how long, it's also how often (as in taking them on schedule.)

Why would someone pay for some of the pills or have some of the shots, then stop or delay too long?  
Are the side effects so miserable?  Is the cost so high?  Do some women just have so many demands on their time from job, family, money or distance that they can't continue?