You are partially right, though. The OS network stack does expose and handle ports if you use a protocol that has them.

Networks are built in layers. There's a physical layer underneath IP, then there's IP, and then there's TCP and UDP on top of IP.

The OS network stack has components that handle all of these layers. That's why it's called a stack.

Port numbers are part of the individual protocol (TCP or UDP) because there are a lot of things you can do with networking, and port numbers don't necessarily make sense with all of them.

For example, when you ping another computer, that uses ICMP, and there is no need for ports with ICMP. You're pinging the whole computer, not trying to connect with one of several applications running on it. So ports are not really needed.