I think mostly it was that the flip didn't have sufficient feature differences from smartphones, as both were fairly limited in how you could use them, whereas the GoPro was more rugged, had waterproof housings, could takee longer videos, was mountable, etc. Also, the GoPro managed a high level of adoption in the extreme sports market which served as an effective endorsement system.

The flip probably could have found a new niche but cisco wasn't interested and basically let them be consumed by the advancement of technology.