Well, Excel has a lot of common use-cases around processing numeric (and particularly financial) data. Since some locales use commas as decimal separators, using a character that's frequently present as a piece of data as a delimiter is a bit silly; it would be hard to think of a _worse_ character to use.

So, that means that Excel in those locales uses semicolons as separators rather than the more-frequently-used-in-data commas. Probably not the decision I'd make in retrospect, but not completely stupid.