Because good dogs can make them money. I don't think you quite understand the kind of money that changes hands at dog fighting events. A good fighting dog is a source of pride to people in Pakistan. Everything from the Bully Kuttas, Gull Terrs to Kurdish Kangals. Or then you have the likes of the Farmers Boys from Northern Ireland who fought, bred and imported/exported dogs throughout the UK, Ireland and all over mainland Europe. In fact, most of the Pitbulls you see on the mainland UK, come through Northern and Southern Ireland. It's not illegal to own Pitbulls south of the border, so they're doc'd as "Irish Staffordshires" which is just a cover name for Pitbulls, transported into the North and then onto Liverpool or Stranraer. Good fighting dogs go for thousands of pounds. The more fights your dog wins, the more you can charge to have it roll against someone elses. The more you can charge to stud the dog out.
That's if you know what you're talking about though and have an interest in Molosser type dogs and aren't just making a thinly veiled snobbish, elitist and racist stereotypical thread...