This is simply so oldschool and lovely at the same time. Might it be the sprites, whose language is so sweet or the replay value, that still holds true today? I think it probably is a combination of all the points above plus how our minds relate to it.
I know at 5.99 dollar it almost sounds ridiculous to make this point, but for slightly less money you already can get Sim City 4, which has alot of mod support. Otherwise this game is through and through oldschool fun. Especially the buildings, which you can get later on did it for me.