Contractions - I'm not talking childbirth, I'm talking shortened words. Couldn't, can't, won't. They are a pretty negative bunch, when you think about it. And like almost everything in English, when you have a good look at them they are pretty queer. If don't is short for do not, why do we say "doent" instead of "doont"? If won't is short for will not, why do we say "woent" instead of "wilnt"?
According to Bill Bryson, some of the strange spelling/pronunciation pairings in English date back to a time when England had a number of more or less mutually incomprehesible dialects. A spelling might be widely adopted from one location, but the pronunciation that becomes prevalent might be from elsewhere. An example is the spelling once and the pronunciation "wunce".
The accents survive but the local vocabularies have mostly amalgamated into Standard English. In most cases local words became extinct after the arrival of an exotic competitor that had some sort of advantage - just like the near-extinction of bilbies in Australia, with the arrival of rabbits.
In the case of words, the new word might have been more intelligible in a neighbouring area. It would be taken up to simplify trade and other discourse. In time the old word would be out of major circulation, maybe holding out in a few quiet corners, like children's rhymes and old people's work songs. Maybe this is how we came to be stuck with "woent" and "doent".