sober simply means "not drunk", so using it for "haven't been drunk for X amount of time" isn't that extraordinary
and looking at google ngram, teetotal is just a much rarer word out of the two (like 100x), so it's just more likely to not get transmitted down the generations (I certainly do not know how to use it)
gadders · · focus · HN ↗
I'm sober right now but won't be tonight when I have a couple of glasses of wine in front of the TV.
NooneAtAll3 · · focus · HN ↗
and looking at google ngram, teetotal is just a much rarer word out of the two (like 100x), so it's just more likely to not get transmitted down the generations (I certainly do not know how to use it)