Stefan Koopmanschap made a very interesting point in his talk this morning at Libertyvasion.

None of the significant open source PHP projects (WordPress, Joomla, Drupal, phpBB, MyBB, OSCommerce, OpenX, blah, blah, blah) are written based on any of the open-source frameworks which are available.

I'd like to have a discussion on why that is.

I'll opine that PHP frameworks are a relatively new phenomenon. WordPress, Joomla, Drupal, phpBB and MyBB are all using really old codebases (I'm not familiar with the code bases for OSCommerce or OpenX). Symfony 1.0 was rolled in 2007, and none of those softwares have received a complete rewrite since then.

But your thoughts?