[unabst]

It's because their guidelines are based on look and feel (aka "design"), not user experience or use case. They basically have no guidelines for the experience. It's all colors, motion, and size. Each product team then goes off and reinvents the experience, and decides to sacrifice the look and feel guidelines in the process.

The Google+ page doesn't even appear to have any breakpoints, which is against their own guidelines:

https://material.google.com/layout/responsive-ui.html#

Maybe those gutters are reserved for ads?