Imported types (ex. from the German states) for printing presses didn’t have it because it was an English only letter. Rather than coming up with expensive home modification (which some did anyway eventually but not en masse) there were easy alternatives because use of th was already established and also the letter y kind of looked like thorn in the fonts of the time so you could also sub that in.
Convenience of just doing a workaround rather than paying more money for a more English type modification won out and with so many using th and the thorn disappearing soon the use of the y that looked like thorn dropped out also.















Just idle curiosity but are basements and underground structures more common in areas high up in the mountains or way up in the north like Hokkaido?
In the American South we don’t usually have basements and they say it’s because you don’t need to dig down far to get past the frostline (whereas in our north they apparently have to dig down a fair distance to get to where the pipes wouldn’t freeze from below and once they’ve excavated that much you might as well get a basement anyway) and we also generally have high water tables that make basements dicey except in certain areas. My grandparents lived at the top of a hill on a plateau or ridge and unlike many people in the south they had a basement mostly cut into the slope of the hill (though it had a door leading out where the slope dropped down so maybe it doesn’t fully count), but even with the somewhat further down water tables there they constantly were running a dehumidifier in the basement due to the moisture and on occasion in heavy storms the walls would seep in water.