There are many, many organisations which use Excel sheets as de facto standard interfaces, or "applications" you have to use, because it's the only common tool

There are many, many organisations which use Excel sheets as de facto standard interfaces, or "applications" you have to use, because it's the only common tool the people with the domain knowledge have access to and are trained in, and sharing them is trivial - just email a .xlsx. I've seen government regulators supply template Excel sheets as the mandated standard by which private companies must, legally, submit data. Being able to interact with those spreadsheets in a sensible language with a front-end that doesn't suck would be huge.