There are tons of travel affiliate programs, but none of them pay squat because the root problem is that "leads" are common, but paying customers are rare. It's a bit of an overgeneralization, but it isn't totally absurd to view the entire travel industry as a massive lead-gen operation for hotels and (to a lesser extent) airlines.

About the only thing you can do in travel is find some way to make something essential (housing, transportation) cheaper than it already is. If you can't do that, you're a middleman, and the game of the middleman is competitive and well-defined.