In protocol design, why would you ever use 2 ports?

Question

When a TCP Server does a socket accept on a port, it gets a new socket to work with that Client.
The accepting socket remains valid for that port and can accept further

Answer 1

In my view, it's just a bad design choice in the first place. In the old ages where it was invented, firewall and NAT were not existing ... Nowadays, the real question is more "why people still want to use FTP" ? Everything FTP does can be done using HTTP in a better way.