Something this API gets right is having a unified interface for both IPv4 and IPv6. With the sockets API, you have to decide for one of them. Changing isn't easy as the constants and structures are all named differently.

While it's possible to use IPv6 sockets for IPv4 connections, this doesn't cover all use-cases. For example, you can't do IPv4 broadcast with an IPv6 socket. Additionally, as most examples are written for the classic IPv4 API, that's what everyone uses per default. Later on, when people complain about missing IPv6 support, they are turned down because it's a ton of work to change.