It is because of the different publishers. DH has always been an indie brand.
I remember when the first AvP came out, it was the best selling independent comic book of all time, it had something like 100,000 issues sold.
Somebody else posted a response saying that was like 200,000 thousand short of what Marvel and DC's high comic series had been.
It is an era thing as well. Naturally the high mark for these issues will continue to increase as more people read them. It isn't a subset of culture anymore, but entering pop culture.