As a Real Programmer who started his career right when the web took off, I can tell you why. At first, web apps were CGI scripts, so back-end only. But most of the jobs were in native applications. At some point you play around with interactive web page, and the DOM is a mess, browsers all behave differently and you give it up in frustration. Swing, Qt, Win32, are all not bad, and act quite predictably. Then you see web apps start coming, but they are slow, and you still have that bad experience from earlier. Then you start reading HN and notice that every six months the new thing changes, and you say, "hm, Swing, Qt, Win32 don't need to change all the time, something about this web app stuff smells like Done Wrong," and you avoid it like the plague. And when you talk to your non-profit friends who are setting up an online store, they are all hiring some guy to do it in WordPress, and it takes 7 seconds to load, 50+ JS files, and 30+ CSS files (I kid you not), and you don't even want to talk shop with that kind of developer.

It's funny you say that, because that's exactly why I avoided it for so long.