I think perhaps we've also partially lost the meaning of ground breaking research given the constant news articles on "ground breaking science" and the constant overinflation and exaggeration of one's papers and achievements.
Yes, and we can’t expect it to occur in a socially confined over-structured environment either. Academia has changed a lot since then, with peer review hell, publishing pressure, etc. I mean, are we really pretending to be surprised that a system of incrementalist incentives produces incrementalist results?
Besides the current structure of research and the known weaknesses (misaligned incentives, funding issues, etc.) science in general today ran out of low hanging fruit. The last unexplored or unanswered riddles may need prerequisites that are outside of the current boundaries so someone needs to open the door do a vast new bubble that has more relatively low hanging fruit.
Also humans probably (don't quote me on that :) ) can't come up with any new questions or answers unless they are already at the edge of that bubble. And they each see and understand a smaller patch of that surface as it expanded. Stumbling onto new thinks is exponentially harder.
This is what those revolutionary discoveries did for us in the past: Opened the door to a new world where the hard answers were suddenly a bit easier, they made sense.