PHP will continue to do well because it is the most extreme example of the "Worse is Better" (http://www.jwz.org/doc/worse-is-better.html http://www.jwz.org/doc

PHP will continue to do well because it is the most extreme example of the "Worse is Better" (http://www.jwz.org/doc/worse-is-better.html http://www.jwz.org/doc/worse-is-better.html) design style. "Worse is Better" software designs (e.g Unix, C) have shown to be far more popular in the market than more elaborately designed systems (Common Lisp, etc).