Oh, I don't know... Maybe because of easiest imaginable deployment scheme? Comprehensive stdlib and lots and lots of libraries and bindings for everything? Its forgiving nature, which makes it try very hard to do what programmer meant instead of dying with cryptic error messages? Or possibly because of bazillion other legitimate reasons people have for choosing to use it...
Languages are just tools. Some are better than others for a specific task. This is a fact. You choose the language for a given task because it fits the task better than other options. That's all there is to it.
I don't currently use PHP, but I acknowledge that there are situations where using it makes sense. I'm just not in one of those situations in present. Saying that PHP is a bad choice in every situation is worse than stupid: it's simply wrong.
"Its forgiving nature", like VB's "On Error Resume Next" and JavaScript's automatic semicolon insertion, is not an advantage. Debugging with cryptic error messages is better than having no idea that the program is silently doing the wrong thing.
Its standard library is no more comprehensive than those of comparable languages.
The only advantage left, then, is the same one all the sibling comments bring up: it's already installed on the server.
So the question remains: Why would anyone who has a choice and knows that other languages exist ever use it for anything?
Languages are just tools. Some are better than others for a specific task. This is a fact. You choose the language for a given task because it fits the task better than other options. That's all there is to it.
I don't currently use PHP, but I acknowledge that there are situations where using it makes sense. I'm just not in one of those situations in present. Saying that PHP is a bad choice in every situation is worse than stupid: it's simply wrong.