How do they still have money?
Their primo offerings can be readily substituted with FOSS since decades, and at this point the libreoffice experience is better.
1. The effect of being the closest-to-reach solution on MS Windows.
2. Organizational inertia.
3. MS Office' use of OOXML is convoluted and difficult to replicate/reverse engineer, making it difficult to perfectly export to and import from it.
4. Fear, uncertainty and doubt about ditching MS Office. Nobody ever got fired for paying for Microsoft Office.
5. MS marketing
1. The effect of being the closest-to-reach solution on MS Windows. 2. Organizational inertia. 3. MS Office' use of OOXML is convoluted and difficult to replicate/reverse engineer, making it difficult to perfectly export to and import from it. 4. Fear, uncertainty and doubt about ditching MS Office. Nobody ever got fired for paying for Microsoft Office. 5. MS marketing