Microsoft Office is one of the most recognizable and valuable brands ever. I'm quite terrible at marketing, and even I can recognize how stupid the rebrand was.
Maybe they figured their brand was too recognizable and valuable, and had to knee-cap it to restore the cosmic balance of the Great Material Continuum.
EDIT:
There's even a rule of acquisition that could possibly apply here: #239 - Never be afraid to mislabel a product.
Literally this. It's one of the strongest names in all of software. It really boggles the mind.
This is the same company that thought it would be an awesome idea to rename "Microsoft Remote Desktop" to "Windows App" on MacOS.
It wasn't. It's the dumbest name ever.