I have my reasons.
Seriously - I do. And they're personal ones. It wasn't a big soul-ripping cultural choice that I was faced with. Why did justamom choose Alpha Chi Omega instead of any of the other organizations in the NPC? Why did you choose Zeta Sigma Chi instead of the NPHC/NPC?
I guess what I'm getting at is that the "why" of this question isn't relevant (to me). It might be to other folks, but I just went where my heart and head told me to go.
(edited to get ZChi's organization name right)