My OS vendor didn't set up my firewall rules, lay out my subnets, or configure my routing. I did that. Twice. Because I've got a slightly more advanced network layout than your typical home user. And that's all much less complicated that what your typical corporate network would be, which is much less complicated than what an ISP or COLO provider has to deal with. And then there's the cloud...

Yeah, sure, if your requirements can be met by a cable modem, then you're basically good to go. Until DNS breaks for some machines and not others, and it's because your ISP screwed something in their IPv6 routing but it still works on IPv4. Or Microsoft's authentication servers decide they don't like your IPv6 subnet anymore and Minecraft refuses to start unless you turn IPv6 off. Or... You get the idea.