Because not every ADS report is recorded by sites like Flightradar24.
Oh, you didn’t mean ADS-B was imprecise but that the collection of ADS-B data is imprecise. Got it, and agree.
ADS-B, which I am perhaps a collection expert since I am a chief architect of data management systems involving ADS-B, is a short range radio signal, so it isn’t going to be picked up in every location. All kinds of tracking systems have been devised, even some you can buy for a personal computer, but it was never intended to be a wide area system.