Comment by johncolanduoni

Many IoT devices (or Windows when the LAN network location is set to “Private”) expose a wider surface area to local network addresses. Having a competent firewall on your residential router is still useful, especially for those that have no idea how to configure their endpoints securely.

Comparing a residential router to a network operator’s router is spurious: those routers don’t perform any sort of filtering for the public internet traffic flowing through them.