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...