I think its the knocks are starting to match their quality for 1/3 the price.
I think it’s more that 99% of people don’t need a gopro. I’m a damn good mountain biker and snowboarder but the footage i would get with a go pro would be pretty boring !!
I’ve also lost plenty of footage using my GoPro, cliff jumps in exotic locations etc, get home and and corrupt video files etc. Turned me off it