Because you are allowing company B to technically enter your home. But for them to do that wouldn’t Company A need a warrant for using Company B to enter your home? The same way as far as I know get a warrant to search pedo’s devices and entering home. I definitely know they need to have a warrant to tap your phone and stuff.
So, I know this isn’t exactly what your situation is, but, it does prove that your beginning assumptions are wrong.
The FBI and State Police send a list of all known “illegal files” to all the ISPs. The ISPs are required(? It may not be required, but it would be hard to find one that doesn’t comply) to report any instance of those files and the IP and owner of the device that received the file.
They will use THAT evidence to get a warrant to physically enter your home and remove any devices that may have been involved.
Those devices will be destroyed after they are scanned for illegal activity, even if there was NO ILLEGAL ACTIVITY FOUND ON THE DEVICE.
Be careful. Nothing you do online is protected.
Also, Fuck the police.