Despite all the above reasons, the main reason for the current zero competition is because for all enterprises,using azure AD is a natural progression from their much abused on-prem AD which has been linked as the primary mechanism for user auth across all kinds of products (MS and non MS). To be honest, MS doesn't have to do anything now. Just sit back and collect the money (and once in a while acquire things that have potential to become enterprisey like the GitHub).
As a side note, this increased use of Docs is unfortunately out of sync with security policy where I work. Certain types of data are only allowed to be shared through an encrypted portal that auto-deletes the file... Unless you put that data in a Google Sheet and hit the "share" button.
I have a free 50 user legacy account with Google Workspace and I only use it for personal stuff. I don't trust it for business.
And to a certain extent, Outlook. But that’s mostly due to sheer inertia.