Conservation biology does focus on the benefits of biodiverse ecosystems to individual humans. In particular it models the way in which reduced species numbers will adversely impact us by degradation of ecosystem services like water cycling, water and air purification, pollination, coastal and inland erosion prevention, carbon storage, and the loss of potential new foods, medicines, materials, and a very wide range of biotechnologies. It's the louder voices in our culture and media with oppositional interests that successfully mischaracterize and drown out what conservationists say.

This is why people often mention "the planet you will leave to your children". The consequences might be too far in the future to be individually impacted, but presumable most people care about their kids future.