Scores of police departments and other government agencies run ALPR cameras, and share the results with Vigilant and other companies so that they can have access to all of the results that Vigilant holds. Philadelphia PD even ran unmarked vehicles with ALPR equipment bearing a Google Maps logo a few years back.[1]
Repo companies and others are sending out drivers in vehicles with ALPR cameras who patrol mall parking lots, apartment complexes, etc and then upload all of that data to one of several companies including Vigilant. These folks can scan 15,000 plates a day without a lot of effort.
Homeowner associations and apartment complexes (or their security companies) also frequently have these ALPR cameras along the paths of ingress or egress.
Universities are using ALPR for parking enforcement (and then selling the data to companies.)
[1]https://motherboard.vice.com/en_us/article/kb77dm/philly-pol...