PHP continues to thrive because of WordPress and PHPBB. There are so many sites running these two pieces of software that PHP will be a top language for years.

PHP is also one of the easiest languages for Designers to learn. If you know HTML, adding a few bits of PHP is easy.

Even if you dislike PHP, (I certainly do) you end up getting good at it because enough projects touch it that you kind of have to be good at it. It is like JavaScript, I don't like JavaScript as a language, but it is essential because you can't not know it.