Because they took upon a very hard task, and kept punching it year, after years, through, low margins, highly cyclical market, extremely low returns on capital, tricky clients, and a marathon like RnD expenditures.
They are the leader because everybody else dropped out, and went to make money on something easier, like making Wordpress websites.
The US moved up the stack. We are a nation of software engineers who are losing the knowhow and knowledge on how to build the things that actually enable software.
They are the leader because everybody else dropped out, and went to make money on something easier, like making Wordpress websites.