My question is why couldn't Microsoft, Google and such have built their cloud services from proprietary code (their own and bought), much like Microsoft built t

My question is why couldn't Microsoft, Google and such have built their cloud services from proprietary code (their own and bought), much like Microsoft built their desktop OS and office and proceeded to dominate that market. I don't see the evidence behind the claim that it "has been only made possible due to almost all software being free/open". MS certainly had the money, and it didn't come from FOSS. If anything, I could see small players like DigitalOcean or OVH struggling to afford the fees for the code they needed, leading to an even greater reduction of competition.