Some of these companies have (local) law enforcement subscriptions, and default opt-in disclaimers throughout their ToS to make it all tidy and legal.

None of them have contracts with, nor can they sell to, federal agencies. Agencies have to provide a warrant, and the processes are verified through each of the companies' respective legal teams.

Their recordings data is not generally available for sale; that's a legal minefield, but there are official channels to go through. Geofence warrants and things like that aren't conducive to real-time surveillance, and the practice of using those types of reverse-search , differential analysis uses of sensitive data is under review by the Supreme Court; it's thought that they're going to weigh in on the side of the 4th amendment and prohibit overbroad fishing expeditions, even if there's snazzy math behind it.

TLDR; They need to pay the company, either via subscription or direct charge for T&M, require warrants, and the use is limited in scope. It's burdensome and expensive enough that they're not going to be using it for arbitrary random "let's scan everyone's doorbell cams in case there's an illegal immigrant!" situations, but if there's a drug dealer, violent offender, or some specific high value target, they're going to use the broad surveillance tools wherever they can.

Exactly, and people almost always share it, so they don't even bother with warrants.

Hell even if you tell them to get a warrant, they'll just go and get Betty next door's footage instead.