Because way back when, before sensible systems, they used base-20, and despite now running base-10, the base-20 is stuck in the language.
Edit it’s sort of in most languages actually, not just to that extent. I mean, English has “twenty-one”, but no “onety-one”. 1-20 have their own numbers in most languages I think, and after twenty you just repeat the first 10 and add whatever tens you like, whereas the French sometimes repeat the first 20 and add an amount of twenties
English has “twenty-one”, but no “onety-one”.
But you have teens? Thirteen, fourteen etc? It’s just that a dozen was kind of special, so eleven and twelve are kind of irregular, but afterwards it’s just ordinary base 10, isn’t it?
Well, English does. Not my native language.
Yes, my point exactly. No “onety-one”, because “eleven”.
Same with other languages.
But “thirteen”, “fourteen” etc, you think are as regular as “twenty one”, “thirty three” “forty five”?
It is base-10 all the way through, but I’m just pointing out that probably at one point in history, even other languages, for some reason, counted 1-20 differently than 20+ numbers and they sort of stuck.