My router shouldn't be part of the ISP's network for it to use however it likes.
I would rather take full responsibility for it and manage it myself even replace it at my expense if it breaks.
Letting them do that is like giving the keys to your house to every utilities company you deal with and permission for them to give the key to whoever they choose. Do you really thrust them that much?
However this is like asking if i trust the people on the street when i go out the answer is obviously not however that is a public place and not my home and I am aware I may be watched.
If I were a hacker i would get employed at these companies and just exploit all the computers connected to these routers.
Or better yet download the entire database with router SSID's, serial number and password that would make for a fun time.
Free internet forever if the don't detect it.