First of all, where did you hear that and who spoke about 'the reason'?The reason I've heard about why they don't build detailed open source FEM models of the WTC buildings, is that they would need it to be independent. This strikes me as a bit of a cop-out, as there's plenty of useful information that can be gleaned from such a model, even if you doubt the motivations of those involved. One can always check it.
Secondly, you get me the structural drawings for the towers and I will get you an FEA done. NIST have access to these drawings so there shouldn't be a problem unless they have something to hide that is. You have seen what happened when NIST finally released the WTC7 drawings. Their analysis is now in shreds and their credibility is shot.
Let me know how quickly NIST get back to you on the towers drawings issue.