Google started this trend of flat icons a few years back in contrast to Apple’s glassy bubble style that they used to have. I wasn’t sold on them right away, but they’ve definitely grown on me for their unassuming simplicity.
Finally got a chance to design my own versions for work... “Accountability for Money, Accessible Justice and Employer of Choice”. They are definitely a lot more complicated than they look to put together. A lot of it has to do with the 45 degree angles of light and shadow play and of course the reductionist simplicity.