But the first C compilers were written four decades ago by a couple of people in a matter of months. And they were not just writing the compilers but also designing the language at the same time.

"When Steve Johnson visited the University of Waterloo on sabbatical in 1972, he brought B with him. It became popular on the Honeywell machines there, and later spawned Eh and Zed (the Canadian answers to `what follows B?'). When Johnson returned to Bell Labs in 1973, he was disconcerted to find that the language whose seeds he brought to Canada had evolved back home; even his own yacc program had been rewritten in C, by Alan Snyder."

-- Dennis Ritchie, who wrote the first C compiler. http://plan9.bell-labs.com/who/dmr/chist.html

Well, but those 18 person-years did their part to allow those person-weeks. That is: I agree, technology got far. But there's a second phenomenon involved: human knowledge. Technology steps happen in generations, often restarting from scratch. Knowledge steps on the other hand most come incremental (well, with some losses here and there). We're standing on the shoulders of giants.