Everyone remembers the first person to break the 4 minute mile "barrier". I bet only a fraction of those people know who the current world record holder is for the mile and what his time is (even though he would have left Roger Bannister trailing distantly in his dust).

Roger Bannister, Einstein, Turing et al were all giants but they are are well know because they were first and made giant strides in specific fields. People are no less clever or gifted today, but it is much harder to make breakthroughs when so much is already understood and achieved. In almost all fields it is currently incremental improvements.