Or perhaps humans are lazy by nature and, since PHP does a very bad job of keeping us in line, the less disciplined of us end up writing bad PHP code. Of course, if we don't know how to write good code to start with, it's not PHP's fault. I think the simple fact that you can write good, elegant PHP code goes to show that it simply demands a more disciplined programmer (or a framework to help with that discipline).
As someone who mainly write (and get to maintain) C# code these days, I have to say C# (nor any other language I've seen) sadly doesn't stop people from writing utter shit code.
It does no doubt seems more prominent in the PHP world though.
Pascal (object oriented) -> C++ -> C# - > PHP
Despite a reasonably strong background in developoing software, I've found it way too easy to build crappy code in PHP. But, I think it's as much me as it is PHP.
Perhaps PHP brings out the evil that is lurking inside of us as programmers?