The commercials where idiots strap their cell phone to weather balloons popularized this... without pointing out that you're supposed to coordinate with the appropriate air traffic agency for the airspace in which your ballon will fly.
Having been tangentially involved with this group for years... Edge of Space Sciences,
www.eoss.org I can say that they always coordinate with DEN Center and keep them apprised of both the predicted and actual location of their balloons and payloads (many of which have waivers for additional weight) and do it right.
But there's a lot of idiots out there who buy the baloons, strap GoPro or cell phones to them, and let them rip.
If the electronics don't freeze or reboot after landing, they use the "Find iphone" or similar software to go find the thing.
Meanwhile it's just a projectile that someone in the flight levels can hit. Totally illegal and nearly nothing FAA can do about it until after they publish their video on YouTube.
And I don't know how much time any particular FSDO spends on hunting people down who do it and educating them. But I doubt they can spend a whole lot of effort on it.