I think it's less to do with homophone confusion and more to do with usage patterns relating the contracted part to a phrase rather than a single word [1] [2].

I think it's less to do with homophone confusion and more to do with usage patterns relating the contracted part to a phrase rather than a single word [1] [2]. By the logic of the homophone explanation, the following exchange should be much more acceptable than a sentence ending with "it's" or "they're", but to me it seems equally strange: "Are you waiting for someone?" "Yes, I'm." [1] https://www.youtube.com/watch?v=CkZyZFa5qO0 https://www.youtube.com/watch?v=CkZyZFa5qO0 [2] https://en.wikipedia.org/wiki/Clitic https://en.wikipedia.org/wiki/Clitic