Microsoft is just amazing at 'helping' companies chose software. If you're already on a microsoft stack at work, maybe running some in house servers, exchange, some other things, and you're partially in the cloud as well, it's a no brainer to get office as well with it, and teams, and whatever else.
Microsoft has an entire ecosystem that works fairly well. It doesn't make much sense to just use libreoffice when Office just works and comes with the the rest of the pie you are eating.