[heriC]

Because Drupal is a mess. It is like a naturally evolved organism with vestigial organisms and the difficulty in refactoring that comes along with it. The hooks are all global in scope. It all works, but it is all over the place. Using Drupal makes me feel productive, but dirty. And to develop any new functionality the Ruby/Rails stack is much faster. So the reason to want something that marries both is to get fast development for new parts, and giant reusable Duplo's for the repetitive common app parts. If I was religious about these things, I would not be developing in Drupal in the first place... :-)

[bonzoesc]

What if the Drupal productivity is directly a result of the messiness?

[heriC]

Interesting theory, but the productivity is almost entirely due to not having to write large blocks of code. For example, in our last project, I didn't have to write an admin interface, users, roles, authentication, tagging, forms and more. The messiness was tangential, not useful.