I have used excel a lot in my career, but I don't think I have ever created or even seen VBA in any spreadsheets. I think it probably varies a lot by domain, but if I were to guess I would probably say that far less than 1% of Excel spreadsheets use VBA. And a lot of spreadsheets that do are probably good candidates to be rewritten in some other tool.
In my opinion, the reason that Excel has such a commanding lead in that space is more due to familiarity, compatibility, and that Excel is still just one of the nicest spreadsheet apps to use.
