Your first sentence can be used for anything: Etale cohomology was a low-hanging fruit because it depended on a bunch of mathematics and technology that Grothe

Your first sentence can be used for anything: Etale cohomology was a low-hanging fruit because it depended on a bunch of mathematics and technology that Grothendieck benefitted from: algebra, the printing press, and modern transportation. Sure, Euler had horse drawn carriages but that is nothing compared to the speed of modern transportation that Grothendieck had available to him.