That's why I wonder why companies or even individuals pay a lot of money for Office 365.
As others have mentioned, it's not just about a word processor, spreadsheet, etc. It's about integration with other services. There is some pretty powerful capabilities that exist in the O365 world that are used regularly by businesses.
Just as one example - I have a Dynamics 365 system that I support that ties in with Office 365. It has a direct tie-in with Excel that my users use to mass-export pricing on thousands of inventory items, update those using a simple formula, and then publish those directly back into the ERP system directly from within the spreadsheet (ie, no having to re-format and save as a .CSV file and then running a secondary import tool - it is one button-push from within the spreadsheet itself). They use this same functionality to create new SKUs as well.
We have a separate financial reporting and budgeting tool that works with Excel where we have various department managers update their expense forecasts throughout the year. It authenticates with their normal Active Directory logins and gives them access only to their own department finances. They can update their budget, and it is published directly into the ERP, where they can continue to track their department actuals against their budget via a web interface. That same web interface also allows upper management to run their own financial reports.
Then, of course, there is PowerBI. If there was no other service offered by O365, PowerBI alone would make the O365 subscription worth it. It is an incredibly powerful dashboarding and reporting tool in itself, and it ties in with all sorts of systems (again, including our ERP and Payroll systems).
I tried Outlook for example and it is really bad compared to free software like Mozilla Thunderbird or other email clients that are available for a small one time fee.
Thunderbird and Outlook aren't really even the same type of program, outside of them both handling e-mail to some extent. For personal e-mail use, yes, Thunderbird is probably simpler to use. Once you get into Calendar sharing, tie-ins with CRM systems or Teams, message archiving, meeting management - there's no comparison at all.
I use Microsoft Excel, but also LibreOffice and Open OpenOffice and can't see that they are worse than Excel. In fact Excel in some ways is worse than those 2. For example Excel uses a single "undo stack" unless you open each file in a separate instance. So if you change some things in several files, you can only undo the change of the last file you changed. It also freaks me out that the "save" icon does not indicate if a file was modified since the last change. Other (no Microsoft) programs often grey out the "save" button if the file has not been modified.
You're nit-picking things here that are generally personal preference. Saves in Excel are pretty quick, so you can always just click the save button before closing if you're not sure if you changed something. Even better - if you're working on a document that's saved in OneDrive or SharePoint, it is auto-saved continuously with versioning anyway, so you don't need to even click "Save" anymore. And the undo stack works the way it does for a reason - many people tend to link data between sheets in Excel, so undoing between sheets makes sense.
Libre and OpenOffice are good products too, but they are pretty limited to fairly basic work. For handling my home budget, Libre would probably work fine (except that I already have access to Excel, so that's what I use). It is when you get into very advanced features (like external data reporting, Slicing/Pivoting, add-ins) that Excel pulls way, way ahead of everything else out there.
Just government institutions in the EU spend €5 billion per year just for Microsoft licenses. I am sure for that money they could develope alternatives to Microsoft products and then use them for free forever. Imagine what you could do with €5 billion in taxpayer money each year.
MS Office has evolved over 3 decades with tens of thousands of developers. Thinking that a government agency could replicate that effort easily and then "use them for free forever" (implying that maintenance would be non-existent) is pretty silly.