Well, among the many answers you might get to this question, the one that sticks out the most to me is Excel spreadsheets do not have a built in REST API and Websocket service out of the box.

Sure you can pay up for Access or Sharepoint, or whatever offerings Microsoft has that do give REST APIs (I’m honestly not familiar with them). But this is free and open source, and anyone can put it on a web server and start jamming :)

I really never like selling my data to third parties. I usually don't consider using online services unless there's absolutely no good alternatives.