[Sistermadly]

I don't see any ignorance in your post, but maybe a little naivete. No two NPHC chapters are alike, just as no two Delta Sig chapters are alike. So by asking us -- folks who aren't on your campus -- what the deal is with the NPHC not wanting to particpate, you're basically making the assumption that this is the case nationwide.

In short, you've basically just asked "why are all black people everywhere like this?"

Instead of asking us what's wrong, have you considered talking to one or two individual NPHC leaders on your campus and asking them what the problem is? And if they don't respond, then you have your answer -- those particular chapters aren't interested in interfraternal relations, and you can rest in the knowledge that you made an effort and can then move on and have a great time with the chapters that do want to participate.

(ETA: I'm not in the NPHC, and I'm not speaking on their behalf, I'm just telling you what I read in your question.)