Re: How on earth
SD cards are still used a lot. However, compact cameras aren't used as much as they used to be, because mobile cameras have improved greatly over the years. Even though the discrete compact cameras themselves have improved, the difference isn't great enough for the casual user to carry two devices around most of the time.
At the the high end, DSLRs and the like have gained faster burst speeds, 4K video, and are generally more data intensive. This means that get best performance, CompactFlash or XQD cards must be used.
SD cards are still the popular option, but they are being squeezed a little from both ends.