I would venture a good 50% of affilate programs are legitimate, in that you can make money given you have enough skills and time. However, very few affiliate programs offer good profit margins.

The effort required for some affiliate programs, and the resulting monetary gain is simply not enough to justify the time. Is this due to merchant greed? Perhaps. However, it may be ignorance as well since the affiliate manager, or company, may not know what a good payout is to attract affilates.

So....where are the really good affiliate programs? These are the ones where folks make a killing. Are they hiding? No, but it does take hunting, and some fortune to find them.

Why don't affiliate managers promote them more?

I think, for most cases, they genuinely try to make their successful programs known. However, they are competing with hundreds of other affiliate managers trying to get big affiliates too (or any affiliate, for that matter!). In other words, their words are lost in an ocean of promotion of thousands of affiliate programs. So, even if successful affiliate programs are promoted by their affiliate managers, it's still like trying to find the needle in the haystack.