I think this is more of a version of the "why have we stopped making good music/movies, almost everything today is garbage?" issue. With the benefit of hindsight, we only remember the greats (and the very worst villains) from past eras. While if we look around today, we see all the people who will never make it into the history books, just like we see all the songs and movies that will never become "classics." Edit:…
Been reading Chuck Klosterman's book, But What If We're Wrong?. Which is partly that thought. The things that get remembered in the global consciousness are not always the people or things we'd expect. It's possible that we have a "genius" right now that will be remembered in 100 years. But due to all the local noise it's hard to see through that and remain objective. Basically we're really terrible at guessing what…
And it makes sense, especially in our times, sophisticated PR (and Einstein enjoyed that, too, in addition in being a genius) just trumps any recognition one might get in a life time, in the short term that is.
If you are not seeking some grandiose recognition (like Newton or Edison, famously) you are potentially a better explorer of the yet Unknown not bothering wasting any energy and being less corruptable by discoveries, you are happy to share with others and helping to bring about.
Off the top of my head: Three examples of rather unknown "geniuses" in physics in no particular order:
Chien-Shiung Wu, Oliver Heaviside, John Michell
One could also argue, as I sometimes do, too, that a genius is just a convenient narrative device in order to highlight and illustrate some important turning point with the historical person serving as some responsible "actor" in bridging over an otherwise complex and often self-contradictory development into a tangible coherent state.