Why is it called a 'touchdown' in American football when the ball doesn't actually have to touch the ground to score?

Unlike a try scored in rugby union or rugby league, and contrary to the event's name, the ball does not need to touch the ground when the player and the ball is inside the end zone.

In 1889, the provision requiring the ball to actually be touched to the ground was removed. A touchdown was now scored by possessing the ball beyond the goal line.

https://en.wikipedia.org/wiki/Touchdown

Yes, and it's strange in rugby union and rugby league, a "try" should really be called a "done", as it results in points (5 in union, 4 in league) when the ball IS grounded by a player holding it. There are other strange terms in sport, too. Like in cricket. An over isn't over until the umpire calls over.

https://en.wikipedia.org/wiki/Over_(cricket)