Because MS Office is a different business than giving away free accounts to collect user data. It provides cloud services for money. I guess MS has much better redundancy mechanisms and pretty much committed to not lose your data.

Well, shit happens sometimes even with people having the best intentions to do the right thing. Though I didn't hear about a single case of MS losing people's data. But I'm sure MS would handle such situations differently than blaming it on a user and just terminating accounts.