What does your client/customer think of you being on Azure? That you chose the crappy solution because your low-tech infrastructure still uses windows, which does not carry a lot of tech cred.
20% of Azure VMs are Linux.
You are not well informed.
More likely the have _something_ which runs on Azure. Fortune 500s are, pretty much by definition, quite large - and probably have tons of departments and sub departments. And at least one of those departments probably has a task of trying out new things, like Azure, by running something on it.
What surprises me is that nearly 20% of Fortune 500s _don't_ have something running on Azure.
(I wonder what percentage "run on" Amazon)
* Most major companies use more than one cloud provider
* "Use" is a very loose term here. It could mean anything from "the accounts team in some branch office uses S3 to back up their Sage data (or uses an online backup service that uses S3 in the back end)" to "they run their main product on our infrastructure".