Why is it to hard to find a front end developer?

As a front end dev, I've noticed the steady increase in job offers. Most of us had the benefit of growing with the technology. Its why when you see a group of Front End Devs, you'll see a group of mostly early 30 somethings to 40 somethings, and not the usual crowd of young faces in other practices.

The biggest problem I see with Front End Development is the massive trove of tacit knowledge it takes. If you have a portfolio that goes more than a decade deep, a junior front end dev might run across a table based layout, or baffled by transparent gifs used to position. Or perhaps its a site made 7 years ago, and its locked on a 960 grid and the jr dev is throw by the "Clearfixes", used to modern frame works that magically clear floats by psuedo elements, and doesn't understand why her/his grid isn't working when she/he forgets to manually clear the floats. It could be even a site that is 5 years old, and relies on wurfl to do user agent detects the baffling usage of user agents at all to detect mobile.

Anyhow, that's just scraping the surface. My standing theory is Front End Development is only a few years away from being divided into more roles as the current bar for knowledge entry is getting to be almost unattainable.