It doesn't. Basically every other mainstream language does it like you proposed, and it drives me nuts, not being able to tell which function comes from the type and which one from a trait. Furthermore, this would be ambiguous if a type contained an inherent method with the same signature as a trait method. The status quo is much better for code clarity — we read code disproportionately more than we write it, so we shouldn't optimize for writing at the cost of readability.
Anyway, feature proposals are off-topic here, their proper place is IRLO.