I agree with the original poster as far as the menus to purchase a ticket.

If a foreigner is presented with a choice of only 2 options (Metrocard and
some other type of card), he won't have a clue of which is needed for a single
journey to manhattan.

$5.00 is very steep for a ride of a couple of minutes. $5 should get you
downtown on either LIRR or subway. But for JFK bound pax, they would probably
have to charge the $5.00.

My guess is that they fear loss of parking revenus.

At Gatwick, it is a no brainer to obtain a single card that covers both the
Gatwick express and the tube, even though you travel on 2 different systems.