The only reason people still need office -- other than a niche of advanced Excel users -- is because no one, despite the last several decades, has managed to make a 100% compatible DOCX editor (not LibreOffice, not Apple Pages, not Google Docs). I'm guessing it's because there are aspects of it that MSFT keeps secret? The only reason I still use Word is because I don't want to have to deal with random layout incompat…
https://learn.microsoft.com/en-us/openspecs/office_standards...
However, the formats are incredibly complicated, because they evolved from earlier formats that represented nearly the entire in-memory state of the editing software. To a first order of approximation, the .doc format _was_ Microsoft Word.
Source: I worked at Microsoft during this time period and helped document the XLSX format.