Amazon (and Microsoft) offering a Linux distribution is about (a) raining in the explosion of distros their various teams depend on that they don't themselves control, and (b) answering insistent cloud customers requests for "What distro do you recommend? Do you support {distro}? Do you auto patch {distro}? How come update to {distro} broke your service/product? Do you not work with {distro}?
Last year many services on Azure went down because they all used Ubuntu and Ubuntu pushed an update that broke for a DNS configuration that Microsoft uses. Having your own distro won't guard you from fuck-ups of course, but you can imagine the difficult conversation Microsoft had to have with their biggest customers about how Canonical can take down your 40 billion dollar business globally?
Last year many services on Azure went down because they all used Ubuntu and Ubuntu pushed an update that broke for a DNS configuration that Microsoft uses. Having your own distro won't guard you from fuck-ups of course, but you can imagine the difficult conversation Microsoft had to have with their biggest customers about how Canonical can take down your 40 billion dollar business globally?