The fact that they make money on Azure made them do some Linux(kernel)-related work. It made them join Linux International. But it's because they had no choice,

The fact that they make money on Azure made them do some Linux(kernel)-related work. It made them join Linux International. But it's because they had no choice, not because they wanted to or suddenly stopped believing in vendor lock-in. If they want to be competitive, they have to offer easy migration options from other cloud providers (Azure Migrate). What is everyone else running? Linux. So Microsoft has to do it, too. What determines popularity? To a large extent, winning the hearts and minds of developers. MS always understood this. As developers changed, MS needed to change the way they talk to them, that's it.