Microsoft converts Office 2019 for Mac perpetual licenses to read-only. versions
(consumerrights.wiki)
There is. Compatibility. Ms has had a monopoly on office for decades, and some things still don't format correctly or functions don't work as they do in ms office.
For most people, laziness prevails when it just works in ms office.
But also for most people, the amount of ms office they're leveraging is 100% functional in libreoffice and the like.
Change is also hard for most people.