In some type of bizarre alternate reality, linking a corporate Microsoft account to a personal Microsoft account so the user can earn “Microsoft Rewards points for Microsoft Bing searches done in their browser or Windows search box while signed in with their AAD account” is seen as a good option to have – despite the security concerns and fact that almost no-one uses Bing or knows WTF “Microsoft rewards” are.

For the rest of us – fortunately we can disable this insanity using an MS provided script from https://download.microsoft.com/download/2/4/5/245c3b59-a897-4ee1-a24d-e0ead9007603/AccountLinkingDisable.ps1

General FAQ – https://www.microsoft.com/en-us/bing/account-linking-admin-faq