Take a dust and water proof smartphone, some of them do 20+ megapixel picture and 4k videos. Why would anyone still use a clumsy device? (except for rare action videos)
Most likely, buying a dust-proof, water-proof, and shock resistant smartphone with 4k video support is going to be a tad more expensive than your entry level GoPro.
However, for the casual user (not doing action shots), you've got a point. What use would my mom have for a GoPro that her iPhone can't do?
