how many big projects are there that use these frameworks? I think these frameworks are great for developers working with private clients with small to mid size projects, but a framework may not always serve corporate interests (e.g., IPS). What framework is vBulletin, opencart, magento, phpBB, or other software using?
But there are dozens of frameworks, some of which serve unique markets. Which one should IPS choose? Which one is the best? What if they pick one you don't know? What if the one they pick and invest towards stops being developed? What if it costs more to work with a 3rd party framework than a custom one, as strange as that might seem (since there are risks and learning and customization costs involved)?
Bfarber already stated why a custom framework is being used.
By the way, did you have Laravel, codeigniter, symfony, or something else in mind?
How can you critique a framework without ever seeing the code first? What if it's better than other frameworks at doing whatever the goals of the software are? I appreciate the discussion, but it seems like it lacks any argument. The only negative issue could be the learning curve in learning the new framework, but that's the nature of software development. Lots of new things come about.
It would have been nice if "consumption" related features were shared across apps. You limit "consumption" in ip.downloads and ip.board, but don't do it for ip.content. It is a really weird user experience.