As far as I know, marriage between cross cousins have NOT declined in Pakistan, its still prevailing but in India YES its on decline there are around 7 cousins in my family and I had been married outside although my three sisters had been married with cousins and they are well.
To cite an example, two of my cousins entered into a wedlock few years back, because they both were in love and the families were happy to get them married.
However, there are certain conditions for Cousin marriage
Case 1 : A ( Male ) and B ( Female) are siblings — A's daughter can enter into a Cousin marriage with B's son
Case 2 : A ( Female ) and B ( Male ) are siblings — A's daughter can enter into a Cousin marriage with B's son
Case 3 : A ( Male ) and B ( Male ) are siblings — Their children cannot enter into a Cousin marriage
Case 4 : A ( Female ) and B ( Female ) are siblings — Their children cannot enter into a Cousin marriage
I have seen many Case 1 and Case 2 marriage in my community and the difference I see here is. During my parents generation, the families used to discuss among themselves and ask their children to enter into a cross Cousin marriage.
However, in my generation, Case 1 and Case 2 cousin marriages are common because, cousins end up loving each other and the two families have no problem in seeing their children date and get married.
Though, cross cousin marriages are considered to be genetically unhealthy for the children born from this marriage, but, no one really cares all these things, when cousins have the family approval to date and marry.
Reference Picture : This picture perfectly depict the Case 1 and Case 2 marriages that are prevalent in my community
Yusuf Bhandarkar