Child,
Hazing is across the board (Black, White, Latino, Asian, Purple, Green, whatever)
It is present in MANY cultures over the past thousands of years and has manifested itself in many different ways.
Whether or not hazing happens is purely on a chapter basis for NPHC and NPC/NIC. I know of NPHC orgs that haze and ones that don't haze. I know of NPC/NIC orgs that haze and ones that don't haze. You can't make blanket statements like that and expect people to take your words first hand.
Also, another reason for small numbers is the proportion of Black, Latino, Asian students on campuses across the country. Except for HBCUs, HSIs, and some California schools, all are major minorities at most institutions...hence numbers will be smaller.
Are there other issues that contribue to smaller numbers? Of course. Is hazing one of them? Yes, it could be, but it depends on the chapter.
Hazing is still very very prevalent in all orgs across the board, and just trying to ban it has never worked and won't work until the culture of what it means to be "Greek" is changed. End of story.
Pledging and hazing have been thrown together into one basket, and now it's a crime to make a kid memorize your history or something. So, hazing will continue because members value their history and "traditions".
NPHC and NPC/NIC have strong anti-hazing policies, but if you look at say DST's website for example you will see lists of people who had their membership snatched or fined, etc. for issues like hazing. The list is not like one or two people either. (Sorry for callin DST out, but it's site that sticks out in my mind the most about members who got in trouble w/ IHQ)
As for secrecy amongst NPHC orgs...yea it's there. Why is it there? I am sure there are many contributing factors:
-anti-Black sentiment on campuses throughout the past century forcing undercover operations
-the sense of empowerment the individual gets being part of something exclusive (this obviously is not limited to NPHC orgs)
-"traditions" building up over time
-probably a lot more too
As AKA Monet said, a lot of the misunderstandings come from much bigger issues like segregation (both self-segregation and intentional segregation) or stereotypes or whatever.
Greek life has the potential to be bridges between various cultures and backgrounds. Unfortunately, right now it magnifies the barriers in many cases (per my research).
It's up to us to change it.