Some of the best programs stay private and prefer to stay that way. Exclusivity is one of the perks they grant their affiliates. First, it is important to understand that the merchant usually makes the sale- not the affiliate. Many merchants complain that their affiliates are not making sales when in fact they have forgotten their role as merchants. Affiliates pre-sell the product and get the traffic to the merchant.
Many merchants simply lack the skills to convert the sale.
Naturally certain products sell better online. Pharmaceuticals, informational products, intangibles, services, unique products and digital products are easier to sell and often have higher margins. Everyone wants to pin success on traffic, which is part of the problem but not the whole problem. First of all it is important to understand that some websites just will not do well with revenue sharing. Many webmasters lack the skill-set needed to really implement revenue sharing on their site.