Why is PHP so popular?
Anything which is simple is initially criticized by people. Take the example of google search interface. Poeple tried with many complex interfaces but all came to same conclusion that the world just need a simple text box for search. I think the reason is human mind does not like complexities. It is easy to extend and share something which is simple.Another example is TCP/IP. It does not provide any QoS like ATM. But I think that shortcoming became its biggest advantage.
Same thing can be said about php. Some people says PHP is too simple and only focusses on views. The data gets mixed with the display logic. There is a lot of talk about MVC programming paradigm. I feel good programmers do not really need an MVC model to code good. Bad programmers will code bad anyway. I have been coding using MVC for quite some time without knowing that it was MVC. PHP gives you flexibilty to code anyway you want. That is what makes it a very popular programming language.