> James Clerk Maxwell united electricity and magnetism with a pen and paper. Einstein discovered special and general relativity in the same way.
They had tabletop experiments (and telescope observations) that gave them the clues they needed
A lot of XX century physics was done in tabletop conditions (in the 19xx) with danger to the experimentalists. Also climbing mountains and capturing cosmic rays with photographic film
We might still have something hidden but most of the low-hanging fruit was discovered already.
If you need a machine the size of a small country to observe an effect, chances are that effect is not going to have many practical applications. If it did, it would have shown up at the much smaller scale of those applications.
They had tabletop experiments (and telescope observations) that gave them the clues they needed
A lot of XX century physics was done in tabletop conditions (in the 19xx) with danger to the experimentalists. Also climbing mountains and capturing cosmic rays with photographic film
We might still have something hidden but most of the low-hanging fruit was discovered already.