Why does the English language name floors differently?

AviatorTom
Why does the English language name floors differently?

OK, we know that US and British English have different names for the same things...

Hood/Trunk vs Bonnet/Boot ; Apartment vs Flat ; Cookie vs Biscuit ; Suspenders vs Braces

But why do the two flavors of English language label floors in a building differently?

Look at the picture. In British English, a person enters a building on the Ground Floor and goes up to the First Floor, while in US English the same person is already on the First Floor when they enter the building.

When a Londoner visits New York City and is told his hotel room is on the 5th Floor, he goes to the wrong floor. Similarly, a New Yorker in London, when told his room is on the 5th Floor, also goes to the wrong floor. OK, the buttons on the elevator might save both of them. šŸ˜

What happened? Why is there such a big difference?

Maybe we should ask YouTuber Laurence Brown of "Lost in the Pond" ... šŸ¤”

Updates
8 mo
In the UK, if the entrance to the building is elevated above ground, say on top of a car park, is the entrance floor still called the ground floor?
Why does the English language name floors differently?
15 Opinion