In the US we use either 1st floor and Ground floor to refer to the same floor. The second and higher floors are consistently named though, except for those buildings that skip the 13th floor.
Singapore is even more bonkers because they have eastern and western superstitions to accommodate, plus it's a really densely-built island so tall buildings are extremely common.
Not always, nothing like the US and inconsistency, I work in the northeast US on a college campus our buildings have G-1-2-3....even the newer buildings follow it.
When your country is made of tiny countries (states) with comparable sizes and populations to European countries there are always going to be exceptions.
It would be if you did it in the US, where everybody knows the ground floor is the first floor. Here in Europe, it's just taught that way from birth, so everybody knows that the first floor is above ground and there's no confusion.
It makes perfect sense if you learn it that way! It's hardly asinine in any case. I don't think it's ever caused a problem, except for Americans in Europe getting confused by it or vice versa.