The problem is that people are lazy. Most people I know don't even read manuals anymore, and you think you're going to get them to look at flow charts? People are able, just not willing to do the more advanced setup when they can just plug it in and be done.
Also, if you look at the admin panels on routers it's a maze and I know most people would just give up on the first screen. For example, I have a Buffalo router and the first thing I see Router Name/Model then MAC addresses, Radio, Mode, Channel, TX Power, etc. Most people don't know WTF this stuff is and as long as the thing works they're not going to care.