Why are they called "apartments" if they are all connected?

They're all stuck together, but in a way that every person has his own apartment 'apart' from the other person's. :]

I think of it as that you have 'apart' of a whole establish'ment. Hence, the 'apartment'.

How did they get "connected" in the first place? Think about it.

Apartment was easier to pronounce than tenement.