...by increasing the hands per hour. Can you imagine how long it would take to deal an 8 deck shoe with every casual player (I hate the term ploppie) squeezing out their cards?
Single Deck game cards were pitched to players long before card counting was even known to exist or be possible. It's dealt that way because that is how card games (like Poker) were dealt. Shoe games were dealt face up to prevent mucking, marking, and card switching. Traditional skills checks via the "Eye in the Sky" weren't even a dream in the 1960's...the eye was some crusty cheater dude with a pair of binoculars up on a catwalk looking through a two way mirror.
Was the original way, as BP says above. Many DD games are now being dealt face up. It's faster for the casino, they don' t have to worry abut cheating moves, and the cards don't have to be changed as often since only the dealer handles them.