Buying a company like Canonical is not a big deal by Microsoft‘s standards. But Canonical is actually a private company. In a private company like a public company you cannot get ownership of a large part of it by buying shares, the consent of the owners is required.
What will be the profit of Microsoft by buying Canonical? Ubuntu is a Linux distribution, it is open-source, and it is not necessary to buy the company that developed it to get ownership of the distribution.
Maybe an event like this will cause a stir in the market. But in fact, users can easily switch to another distribution after that. Based on Ubuntu, Microsoft can now develop another Linux distribution under a different name with a substantial investment, without any legal hassle, and at a much lower cost.
And Canonical has nothing but names. It is a company that pays regular losses.