The idea was that time and again Microsoft's OS division would anti-competitvely design internal APIs in DOS and Windows that its App division would leverage. There were also instances where Microsoft subtley broke DOS (and maybe even Windows, but definitely DOS) for competing applications. People used to talk about "undocumented" API calls.
In the end Microsoft's OS gained proper competition through the paradigm shift of FOSS, specifically with Linux. Microsoft helped a key competitor (Apple) off its knees and look where we are now – Apple has a mobile OS, Microsoft has none. Microsoft didn't board the internet/web train quick enough, didn't forsee how big search and social media would become (in fairness, a vanishingly small number of people did) and so now they have Google and Facebook to compete with. Amazon parlaying their experience from a building an at-scale marketplace to a cloud-computing platform took everyone by surprise.
Back in the day I lamented Microsoft's stranglehold on the software industry. They are still a behemoth but they no longer have the stranglehold they once had. Amazon has competition. Does Amazon unfairly leverage its marketplace monopoly to crush competitors? If they do, prosecute them. If they don't, out innovate and out compete them!
Will Google's stranglehold on search ever be broken? Maybe we'll have to think laterally. Like distributed open-source search. Will Facebook's hegemony over social media (FB, FB messenger, WhatsApp, Instagram) ever be challenged? Do we have the luxury of finding out in a decade or two like we did with Microsoft? Microsoft never amassed the data on their "customers" that Google and Facebook and every Tom, Dick, and Harry do now.
Of all these companies I intuitively feel that Facebook should be broken up. Into its constituent social media parts, that is. Either that or legally mandate interoperability so that we can move to a federated social media landscape to encourage genuine innovation and competition. We need the global equivalent of the ITU but for social media.
Amazon are scary but that's only because they are bad-ass. If they break the law, fine. If it turns out in a decade that it hasn't been possible to unseat or challenge the enormous tech incumbents with FOSS challenges then maybe we ought to take a serious look at the economics, social dynamics, and network effects involved.
edit: clarity
edit ii: could people who have downvoted my comment explain why please?