I can't comment on the Google integration, but with Office that's actually a limitation imposed by Microsoft, not Dropbox, and it is documented.
https://help.dropbox.com/installs-integrations/third-party/microsoft-office-faq
Do I need a special license to edit my Dropbox files in an Office Online application?
If you have a Dropbox Basic or Plus account, you will not need a Microsoft account or Office license to edit your files.
If you have a Dropbox Business account, you will need an enterprise Microsoft account with a license that allows editing in Office Online (Business, Business Premium, ProPlus, E3, E4, or E5).
Additionally, if you're using a tablet larger than 10", Microsoft requires that you have an O365 license to use Office applications.
... View more