It’s would be a trivially small amount of money for Apple to create an internal group dedicated to proactively finding and eliminating scam, copycat, infringing, exploitive apps. But every one it finds costs Apple money. And doing nothing isn’t hurting sales, not when it’s so much cheaper to just market the App Store as so secure and trustworthy. Apple seems to view App Store trust and quality as a marketing activity more than a real technical or service problem.
Jason Cross is absolutely correct. Whenever you hear one of our tech megacompanies say “Our platform is simply too big — we can’t effectively fight abuse” (of whatever kind), what they mean is “Our platform is simply too big — we can’t effectively fight abuse without reducing our profit margins.”