Kinda like it says, they get it from fleets, app makers, etc. For example, you might put an OBD2 device like Automatic in your car to lower your insurance - the company making the OBD2 device might be selling location data of that OBD2 device. Commercial fleets have those as well, and that data is also sold. Same for mobile apps - a lot of them collect user location data, especially anything related to motion/navigation.

One example - http://www.coyotesystems.eu/ but there are dozens, if not hundreds, more companies selling this kind of data on their users, and companies like Inrix aggregate it.