Many of M's changes are "under the hood" and less obvious to the average user. If you compare a Lollipop handset and Marshmallow handset side by side, the user

Many of M's changes are "under the hood" and less obvious to the average user. If you compare a Lollipop handset and Marshmallow handset side by side, the user experience is very similar. M wins, but the differences are more subtle than, say, the Kitkat-to-Lollipop transition or, especially, the Ice Cream Sandwich-to-Kitkat transition. The other factor at play is that people are using larger, more functional handsets than ever, with larger batteries that are going to take longer to wear out (albeit, increasingly non-replaceable batteries). Screens are more scratch-proof and cases are preventing breakage. A 5 inch phablet from a year and a half ago is still pretty functional today and has replaced people's 9.7" iPads for many day-to-day uses. People are not replacing their devices at the same pace as in 2011. Plus, it's going to be months before OEM's get around to updating their huge installed base. I wouldn't hold my breath.