Then there is usually a chapter on IPv6 that just briefly covers the differences.
I.e. the exercises all tend to use IPv4 as the foundation so people don’t practice v6
IPv4 is, for all intents and purposes, still the default transport. It’s also simpler than IPv6 in some regards. When teaching layer 3, it makes sense to teach both, and teach IPv4 first. Though I fully agree that they should be taught with equal emphasis. I don’t doubt there’s a good number of programs out there that don’t into sufficient detail on IPv6.
IP addresses show up everywhere when you are working with both TCP and HTTP. Sockaddr is all over sockets programming, IPs show up in HTTP headers, etc.
They absolutely care about the underlying protocol because the underlying protocol is how you address the other end.