1999 and 2002 correspond roughly to telecom and dotcom bubbles popping. So open source operating systems were also pulled up into these positions through a lot of work and by the early 2000s it was kind of obvious this was the way forward.
2008 financial crisis really knocked the high end (RISC/UNIX/Itanium) and started the long migration to renting vs owning. In hindsight it's remarkable how much money used to just be there in the economy of all this. But I guess it still is, considering how expensive public cloud is.