The reason for a lot of homographs with ASCII is that there are old code pages that have entire non-US alphabets and punction sets in the 128-255 range, and regular ASCII in the 0-127 range.
It's a design goal of Unicode to support exact round-trip transformation with any code page ever in use in the real world, so they can't unify two characters that appear at different code points in a greek codepage without breaking things, even if they're always graphically indistinguishable in a font.
It's a design goal of Unicode to support exact round-trip transformation with any code page ever in use in the real world, so they can't unify two characters that appear at different code points in a greek codepage without breaking things, even if they're always graphically indistinguishable in a font.