I guess everyone accessing the same data at all times is not so valuable after all.

I've seen people having multiple versions of the same excel file and not remembering which was the last one...

I agree with most of the answers already posted about why Excel is so ubiquitous. To respond to this comment specifically, though, I'll just mention that we use a product called EASA to enable us put a web app on top of critical spreadsheets while also connecting to a database i.e. you can "de-couple" the data from the logic. There are some use-cases that describes this here: https://easasoftware.com/case-studies/amlin-reducing-risks-e...

...and here: https://easasoftware.com/case-studies/leaseplan-transforming...