Kind of like how in physics people tend to say "why doesn't anyone make truly big discoveries anymore?" It's because the easy targets for modeling and connecting have all been looked at for the most part. There aren't as many "unexplained effects" in our every day world that people can readily study with every-day means. The edge of discovery has been pushed to the world of high-tech instrumentation and simulation.

With medicine, the easy-to-cure stuff has all been tackled, we made anti-biotics that cured a massive amount of normal, killer diseases that plagued us for a million years. We made vaccines for viruses that don't constantly spread and evolve like polio and measles and so on. The ones we're having the hardest time with are the very complicated ones.