@mr zambia - when a wanker quotes research, especially a loud mouthed on quotes research, it is coomon practice to state the research and where such research has been published, by whom and how such publication can be accessed. Failure to do so renders your statement void and a lie. Based on your inability to read more than three sentences, I'd not hesitate to say you're trying to wank us all off with your "research". WANKER!
If you stand at the KFC food court at 13:00 hours today and see the numbers of people consuming KFC products the answer to the question asked in the topic title will be answered.
People are hooking up with other people for three reasons, same as the reasons they are eating KFC, Hungry Lion, Steers or any fancy restaurant food:
1. Means - becauce they (legally) can
2. Opportunity - because the products and/or individuals they want are within physical reach
3. Motivation - this comes down to (among other things) personal preference, quality, quantity, prestige, prior experiences, tales told, whims, fanciful expectation, man love of experimentation, "jungle fever", ...
The question is as silly as asking, "why are some people quenching their thirst with river water instead of rain water/sprinmg water/ tap water/ well water / fruit juice / liquor / liqueur/ piss/ salt water ...?"
Next the person will ask "why are certain women attracted to "Bobby East" sized dicks instead of micro penises?" Why do people pick coke over fanta, chibwantu over maheu, light women over dark skinned ones...
The more educated and wise questions may be "What are the effects on the extended families of inter x hookups?" (x could be racial or generational or educational or national or tribal ...)
Leave the couple out of it, speak for yourself and other wankers "affected" and say "what is the effect on wankers outside the relationship between two adult lawfully wedded people?"