Not arguing for PHP here, but it has at least four things going for it that other mainstream languages don't: low effort config, ubiquity, utility, and a short learning curve. The newbie adoption experience for other mainstream languages and frameworks has a lot of friction. And over time, the tools become more complex making newbie adoption that much harder (I'm looking at you rails). There are some efforts at helping with this (e.g. Yehuda Katz's promising Tokaido). But that's the exception, and it seems to me that the real solution to taking down PHP is providing an easier on-ramp for novices.