As others have stated in various discussion threads, smart station owners and companies like iHeart and Audacy not only have terrestrial stations, but have also invested in apps, streaming and social media. It only makes sense that "radio" reaches more people than TV as many people listen to radio while at work, in the car, at home, while working in the garage or workshop, etc. Conversely, to really reach people effectively, in most cases TV requires the viewer to be positioned in front of their set and watching, which most generally happens at home. Granted, some have their TVs on in the background, but if that's the case, when speaking of advertising specifically, their eyes aren't seeing the product being sold if they're just passively listening. Also, as has been mentioned elsewhere, that "TV" audience isn't just watching broadcast or CATV. Many are streaming content, watching stuff they've downloaded or otherwise accessed, etc.
"Radio" can of course mean many things as well, and doesn't just refer to OTA terrestrial broadcasts on stations in the market where that particular listener is located.