Comment by AnthonyMouse

It's the ease of use for medium customers. Large customers have Linux servers with full-time staff to write custom code and do whatever they want because they have their own resources; Facebook doesn't use Azure. Small customers buy a Macbook or Chromebook or tablet and have a gmail address and host their website on WordPress or one of those awful (but easy to use) web host proprietary site builders.

Medium businesses are big enough to want to have their own email domain but not big enough to want to implement their own spam filter, so they turn to the likes of Amazon and Google and Microsoft. Then Microsoft's advantage is they can manage and integrate with your Windows devices. Otherwise they're just doing price competition with every other hosting company. People who aren't even using Active Directory start to wonder why they should pay extra for SQL Server instead of using Mariadb on Linux, and in turn why they shouldn't put that VM on AWS unless Microsoft cuts them a better deal. (Which is presumably what happened with Apple, but offering long-term discounts is not how you make a lot of money.)