It’s not so arbitrary. I’ve grown up in a country which uses commas, but it’s still really confusing even to me, when writing e.g. f(1,2). Is that function applied to 2 arguments or 1? For this reason I always use period as decimal point.
Maths is typically written fast, so subtle spacing is too weak a signal to distinguish meanings. Where I studied maths, we even crossed our zeds horizontally to make it easier to distinguish from carelessly written 2s. Similarly, even though the country uses commas, the uni uses periods, for the benefit of clarity. Almost noone uses semicolons in function application in writing.
