But they thought that because they have a dominant share in the market, nobody could compete them. They go lazy, stopped innovating and expected their market position to keep them on top. Then Microsoft came up with something new and better and took their position. But that does not mean that it is going stay like that. A dominant position today can be gone tomorrow because new competitors and companies are always free to enter the field. Already existing competitors can combine to ruin a larger rival. New ideas and technologies replace the old ones. So even strong and successful company like Microsoft has to fight to keep that great position.
On the other hand, Microsoft is not the largest computer company in world. What is happening here is that there is an operating system, that people have the choice not to use, but they choose to use it anyway. And that is not monopoly. The reason why everyone is calling Microsoft a monopoly is simple. It is because it is a perfectly reasonable thing for the competition to say. Not because it is true, but because Microsoft is their competitor and they want to hurt them. Since Microsoft is so huge, every single computer or software company is a competitor of Microsoft. If Microsoft has a huge market share in something, almost every other company in the industry hates it. The ironic part is that they couldn't pick on Microsoft if it was a monopoly, because monopolies don't have competition.
Another possible factor why so many people call Microsoft a monopoly may sound somewhat awkward. They are just jealous. But to me, this version makes far more sense than most of the other ones. There are people who hate wealthy business owners, just because they are jealous. It could also be because they feel, that earning money is a way of measuring what they are worth and they might feel bad because someone is making more money than they are, and therefore he or she is making them look bad or less respect. And who is more famous for being a billionaire, than Bill Gates. What's more, he has made all the money himself. It is not like he inherited the money or won it in the lottery. He has earned all of it. Most of the people are thinking that he is big, powerful and important and that they probably cannot do the same. And then, they might think that it makes them look bad that he is doing so well and they are not. But it does not only happen in the Microsoft case. This kind of jealousy can be seen every time when someone who is making more money happens to mention it around someone who is making less.