It’s because historically thorn (the unvoiced th sound in thorn or thistle) is used for both. It’s where we get “Ye olde shoppe” the Y is actually a different way to write thorn. Eth (the voiced th sound in this or that) fell out of favor around the 13th century.
Interesting ðat you don’t distinguish ðe sound in “ðe” and ðe sound in “þing”.
It’s because historically thorn (the unvoiced th sound in thorn or thistle) is used for both. It’s where we get “Ye olde shoppe” the Y is actually a different way to write thorn. Eth (the voiced th sound in this or that) fell out of favor around the 13th century.