XLSX is actually a decent format for business users. The only trouble is it has tons of limits [1], most restrictive being the limit of 1,048,576 rows by 16,384 columns.

I'm working with a client who had to split up their data into several XLSX files because they hit a row limit.

They can of course ETL the data into a real SQL database, but ETL tools for end users are still not a common thing plus not all end users have access to a SQL database.

[1] https://support.office.com/en-us/article/excel-specification...

I'm talking about business to business transactions, as in automated transactions on VANs and similar data interchanges.

The industry doesn't really use XLSX or XLS because they're unreliable to parse without Microsoft's Office libraries which require Windows licenses, and the two formats have a huge amount of overhead compared to XML formats and CSV (which costs money on VANs).

This is a space where plain text files and binary is still king. Formats like EDI are still massive. In many ways CSV and XML are the new kids on the block.

Only end users are sending Excel formatted files (and PDFs) to one another.

> The industry doesn't really use XLSX or XLS because they're unreliable to parse without Microsoft's Office libraries

XLS yes, however XLSX is just easy to parse if you document only contains simple types. of course with embedded mathml/wordml it gets a little bit wierd.