Because each manned mission is a solid footprint for our space program, and we don't need to perform the same manned mission 100 times before the Moon Landing.
Not disparaging you guys in your happy moments... (more so, because we're no where close, right now).
But, in your own thinking you are comparing with USA (or the erstwhile Soviets).
Both of those space programs were proceeding much faster .... and that too when the elecronics technology was really poor.. ditto with computing power and all other technologies.
US was taking moon shots at this stage of their program... with 1960s technology.