And, for the most part, sites look terrible.
It’s not that simple, though. While mobile (a.k.a. small) devices have been leading the way in higher pixel densities, they also tend to have Internet access at speeds rivalling a carrier pigeon, and the amount of data included in their plans before insane pricing kicks in is frequently still measured in megabytes. All those double-resolution assets might look great, if (and only if) you have a screen that can render them, but they are also slowing things down and eating up people’s data allowance. Not everyone is going to thank you for that.