@elicin >A lot of ISPs have their router backdoored
All of the ISP routers are backdoored, as otherwise they couldn't remotely push configurations and updates.

ISPs often make it hard to use your own router by refusing to tell you the PPPoE username/password and/or ensuring either that there's no bridge mode on the router, or that it doesn't work.

In the worse case you have to do double NAT (yes, IPv4 only and no IPv6 feels), but that's better than letting the ISP control your LAN.