[LanceH]

The primary reason is that with sans serif fonts there are fewer pixels to send. This isn't really a big deal until you get to the size of Google or Facebook and it really starts to add up.

[amyjess]

I just wish they'd at least use a humanist sans.

I was really sad when Google switched Android's default font from Droid Sans, a humanist sans (and the direct predecessor of Noto Sans), to Roboto, a neo-grotesk.

Or when Apple went from Myriad to Helevetica Neue and San Francisco.

I just really hate everything about the way neo-grotesk fonts look, and mobile UIs have looked awful to me ever since.

[LanceH]

I think for Apple is was more about it being organic and locally sourced.