Well yeah, that's what a NAS is. What you're talking about is just self-hosting a all-in-one server, like people used do with Windows Small Business Server, and all the problems and limitations that comes with.
And plenty of small businesses and hobbyists do that, and then after they "setup and forget" it they get compromised or lose their data a few years down the line.
Yes and no. I've been in companies with windows business servers that were a constant pain to manage. Whereas the modern NAS, Building on stable open source software mostly offers the 'just works' experience people are looking for + the business grad documentation.
Why would using a NAS (or small server) mean ignoring any basic logic (and business requirements) and not having off-site backups?
SBS server "just works" if you just set it up once and then ignore it, your requirements never change, and and don't do basic things like maintenance and installing updates as well.
People absolutely should be setting up offsite backups. And more importantly, testing them so that they can prove that they work. But if they have no technical team then neither of those things are going to happen.
And plenty of small businesses and hobbyists do that, and then after they "setup and forget" it they get compromised or lose their data a few years down the line.