>>88980618Because they're pronounced exactly the same in a non-stressed position. As far as your speaking brain is concerned, they are the same word. Spelling is artificial and secondary it's not a part of the natural language faculty per say (se).
Then, because all of "could", "'ve" and "of" are auxiliary words without a non-contextual meaning, they tend to mush together based on how they sound. Same with "you're" and "your", but probably not with "eight" and "ate" because the moment you start writing "he'll come at ate o'clock" your brain goes like "wait that doesn't make any sense".
