It’s not a complete explanation, but I was awed by the precision of the shower screens used in modern rocket engines. In the 60s it might have sufficed to just spray fuel into the combustion chamber using some nozzles, but now we have highly precise matrices of micro-perforations that maximize combustion.

Also if you want to harden the rocket against EMP attacks you need an inertial guidance system, and those things also demand extreme precision.