FWD is cheaper and gives you a flat floorpan - that is the primary reason why it was adopted.
Well, it's supposed to be cheaper on gas since the engine is pulling you forward instead of pushing.
But, I've been in a few North American cars which, despite being FWD, have a big hump going through the middle for no good reason, the same as if there was a drive shaft to the rear wheels.
It made absolutely no sense, and the only thing I can figure is the car company decided it would be more expensive to retool the plant to actually give this flat floorpan.
I've also seen several cars which still more or less put in a rear axle (even if it's not a drive axle) when you'd be better using independent suspension. The Pontiac Aztec and I think some of the Dodge minivan type things are good examples of this.
Except for at the higher end, some car companies are lazy, stupid, and cheap. And you still end up with a senseless hump in between the rear passenger seats, or a ride which is made silly by having a rear axle (try driving over a speed hump diagonally in a vehicle which has an axle, you'll see that the whole vehicle moves when it doesn't really need to).