If you look at all the live air traffic on Flightaware, all of the information is being provided by their user community by people just like me, literally thousands of people all over the USA and around the world....
If you have a Raspberry PI, flightaware allows you to sign up for a corporate account for free, you download and install their software on your Raspberry PI, connect up a Antenna to the Raspberry PI and you will start to gather data from planes flying around your location, that data gets uploaded in real time to Flightaware to populate the maps you see.....
My installation is about average and I gather information from around 200 planes aware at distances up to 200 miles away....
Some users have better antennas and have them installed higher in the air and can dwarf my numbers......
actually it’s 2000 planes per day
Try ForeFlight.
You can monitor traffic all over the country, and it’s in real time.