You are mistaken in thinking that dense fuel is something nobody else wanted to try. USSR did that in the 1970ies, they have even developed a special high density fuel (syntin) but stopped using it in the 1990ies due to high cost of it.
Sorry, I should have known that most readers would not be up to speed on what SpaceX has done, and I should have explained densification as they've done it. While the Soviets used a chemically denser hydrocarbon, SpaceX has made conventional LOX and kerosene denser by cooling them to a lower temperature than is necessary just to liquify them. LOX gets almost 10% more dense and kerosene about 2% more dense, and they have changed the size of the LOX and kerosene tanks relative to each other so that the ratio required for combustion remains the same. This is just through refrigeration, rather than the more expensive process of molecular synthesis employed by the Soviets.