General answer: there is little motivation for a projection that is about explaining agreement. It works, but Minimalism is about minimal structure including removing projections, not adding them because they work. (Minimalism is, though, a testing ground for theories, so potentially they will be added back in after this re-shuffling of the parts of the theory is done. Not that I'm saying in this case they will.)
Minimalism also uses a different operation, Agree, to deal with agreement, so that might more directly answer your question.
