Welllllllllll...... If you compare your standard 4 Port home router for something like a small SonicWall, FortiGate, Sophos they usually have at least 8 ports.
On the other hand many cisco routers only have 1 or two ports since they assume you use switches w/ vlan colors.
It's the added features like proper ACLs, the ability to connect to more than 3 subnets (business usually got wan, lan and sometimes dmz), use proper routing tables or dynamic routing protocols. UTM features since most of the time they are bundled with firewalls and an overall higher session limit.