Being good at other things can have them generate enough money to blow trying to be good at a $NewThing that smol players only doing $OneThing can't hope to match.
People aren't using Google Drive for the Drive per se or the crappy online file system UI, they're there for the apps: Docs & Sheets are the killer apps: good enough as a word processor & spreadsheet combo for any basic tasks, real-time collaboration that is still first-class and maybe unmatched (or at least the closest matches I can think of are still American vendors), and plenty of people are educated in their use, especially anybody who went to school any time after 2008. Also you know, Gmail: still a great webmail service, and part of Google Workspace too.
Uuuh says who? I think they dominate because they are in fact better for business for one reason or another.