The last time I checked, US property rights made it clear that you cannot just store stuff on other people’s land without permission, and then complain when they throw it away.

They could try to argue that whatever contract the previous owner signed still applies, but for that to be the case, they would have had to amend the deed to the property, and that should have been noticed by your title agency.

What the actual fuck?! Why would you have cameras inside your house to begin with, let alone ones that upload to “the cloud” and let alone ones that upload to users you don’t control?

I’m totally shocked by this.

No, that's how ownership of internet accounts works. Ownership of real estate is based on completely different principles; there is no earthly reason you'd need the previous owner to be involved. Who owns what real estate is a matter of public record.

Doesn't mean they need to be kept in their current location though. You're entirely within your rights to remove them and leave them in a safe place for them to retrieve at their leisure.