Optionally, one could include a discussion of why one should use PHP, but I realize there is convenience and brevity to be gained from simply assuming you are talking to an audience that is already sold on PHP, rather than Java or Ruby or Python or Clojure.
Why PHP?
Seriously, it does not take the conversation forward.
If php is to advance we should welcome all tools that evolve it.
http://www.chrisshennan.com/2012/02/16/symfony2-and-sonata-p...
http://sonata-project.org/bundles/
For those who don't know what a Symfony bundle is, you can think of them as an attempt to bring something like Rails Engines to the land of PHP.
That and keep in mind there are many projects that don't need something like Symfony or Zend. A lot of projects that is the same thing as using a sledge hammer for a thumbtack. Something like Laravel gives me the tools to get a small project up and running quickly without having to do a lot of the mindless/repetitive tasks we all have to do with new projects.
Lastly, your "solution" that gets your attention is nothing new. It is not web development, it is installing software via a web interface. So you say what does it solve when really you are just asking for another e-commerce and CMS solution. Hmm, that hasn't been done thousands of times before...