When it comes to reading email on mobile (the world's dominant platform), we're all like over-amped weekend skiers schussing the blue runs. All we want to do is go straight down as fast as possible. Over and over. What we do NOT want to do is have to decelerate and make a bunch of awkward wide turns all over the slope. That's no fun at all.
But that's what email that has not been formatted correctly for mobile forces us to do.