The reason is simple: PHP is getting better. It took a long time, but people owe it to others and themselves to help PHP thrive because it can only get better with the help of others. Frameworks like Laravel are somewhat responsible for the resurgence in PHP development, it's becoming an exciting language to use again, the quirks and issues the language had are slowly but surely being fixed in versions post 5.3 that's for sure.

You have to remember that no other language has really been able to beat PHP in terms of ease of use and setup. Every shared host in the world has PHP installed. There's no server to start, no scripts to run, you just upload your files to the server and they work. Django/Rails and all of those other languages don't just run on most shared hosts. PHP is easy and that's part of its appeal and the reason why it won't be dying any time soon.

Every language has quirks, not just PHP. If you want to talk languages that were too, once horrible and in some ways still are, look no further than Javascript. That didn't stop it becoming the most widely used scripting language on the web.