That’s because almost any legal to sell consumer device gets an FCC certification. It can still cause interference, but within limited parameters that significantly limit the blast radius. Most of the interference people experience will be very limited and almost exclusively due to misconfigured or defective devices. Ham operators run into this occasionally and if memory serves correctly, there was a chapter in the ham license exam about how to identify potential bad RF source and how to handle it (the FCC usually recommend politely letting the person with a bad transmitter know that their TV antenna or generator or whatever is causing RF interference before you involve the authorities as most people who encounter this are simply unaware)

The situation would be very different if it were commercially legal to sell devices that are designed to let you broadcast to anyone without FCC certification on the device or enforcement from a governing body. A billion startups would be selling “communicate with your family across town for free” devices that can easily render emergency services radios useless in a city.