Because it usually is an issue of titration or mask fit.

There are some cases of people have complex sleep apnea, or having awfully non-compliant airways that require uncomfortably high pressures. But the vast majority of people can tolerate PAP just fine.

There are certainly improvements to be made. And thankfully some of them are being worked on (e.g. VCOM or KPAP). And some people could benefit from bilevel or even ASV, and it's a shame that those are often way harder to get. But even if we're being generous, the article's suggestion of 22% of patients who can get by on just the drugs is incredibly underwhelming compared to PAP.