A lot of people use Microsofts products out of old habit and because they are simply not aware of any alternatives. I have helped alot of people try LibreOffice, which offers everything they need from their office suit. Most people also like that LibreOffice looks like what Word and Excel looked like before Microsoft changed up the menu system.
This is an incomplete take. People use MS Office because everyone else uses it. In practice, that means if you try an alternative, then there's no assurance that your documents will render or function the same way on an MS Office installation.
I tried going all LibreOffice when I was a grad student. I had to write a tech report to submit to our funding agency, using a Word template they require. It looked great on my computer. But when my advisor reviewed my document on his MS Office installation, the formatting was all wrong and unusable. Ditto for spreadsheets and slide decks (I can't count the number of times Google Slides mangled my PPTX formatting after I accidentally opened the file in the browser and it auto-saved). That's the reality of doing non-trivial work with external stakeholders if you're not using MS Office.