The official excuse is that those renderers do not include the editing experience they want to provide. But of course Microsoft doesn’t mind that this way they

The official excuse is that those renderers do not include the editing experience they want to provide. But of course Microsoft doesn’t mind that this way they can ignore any standard they want and dictate what features work and what features aren’t available, all without even needing to publish any specification about how it works. The specification is ‘what you see in Outlook is what you get, good luck!’.