And then you want to automate or do some nice charts, and there is Power platform just around the corner...
and then you find yourself limited so you go Azure Functions... and then start one VM on Azure...
Power Platform is for "power users" to be able to "no code" things, this is targeted (MS Claims) as non-IT Users, as is the Rest of the office/Microsoft 365 stack
Azure (including Azure AD) however is targeted at IT Staff, dev's,sysadmins, etc. There is a clear line in how the tools are marketed, deployed, licensed and utilized
After that, you already have some firewalling and VPNs in place so adding the odd server is just a step away.
Adding dedicated lines and firewalls and rules and all bella and whistles with all four big players (AMZ, IBM, MSFT, GOOG) plus 2 ISPs adds cost fast, so you typically pick 2. MSFTbis already there for O365 so yeah, they have a head start
My gut reasoning is that cloud infrastructure is not the same product as office productivity and the two use cases are not the same, the purchasing decisions aren't made by the same people (except at scale, I guess, I'll concede that), and the boots on the ground building shit in the cloud take the path of least resistance where that logic would never apply.
I don't really subscribe to the belief that a company should half ass a product or acquire something in a new market because they aren't already there, but I may be in the minority. Amazon has shown they can build a trillion dollar enterprise without caring about office productivity or chat, but they'll sell the shovels to anyone who wants to try and dig those holes.