It’d be hard to keep individuals from doing this. But individuals aren’t running networks of cameras. Companies are. Those companies probably couldn’t fly under the radar selling LPR data if the practice was banned.
Most individuals I know only have access to a handful of places they could put ALPR devices. Their home, their work, a couple of really really close friends who trust them enough to let them setup a camera on their property. Individuals could pay people to host their cameras but then that starts looking like a business, so while it's theoretically possible for an individual to have a network of APLRs just for the fun of it, that just seems like weird enough hobby that, I don't have any evidence of this, but I don't think anyone is doing that.