The blog post describes only the billing advantages of the "single vendor" approach like AWS or Microsoft. But the other half of it is much more important, and

The blog post describes only the billing advantages of the "single vendor" approach like AWS or Microsoft. But the other half of it is much more important, and that's the security/compliance aspect. You know that anything you buy from AWS or Microsoft is engineered to a common set of security / privacy standards, and that whatever those standards are have been audited by governmental customers etc. Of course they're not perfect, but there is a definite increased security risk in having your corporate data sit inside 20 different companies vs. 1.