estherh- I don’t think anyone actually uses the cards in lieu of the mitzvah. The mitzvah is to give 2 prepared food items to 1 person. Once you’ve been yotzei by giving to 1 person, why not give cards to the others on your list?
A lot of people can’t really afford more than the basics these days and by giving someone a card, you cut out that awkwardness that comes with not giving to someone who gave to you or otherwise expects something from you. Also, I don’t know about everyone else, but the LAST thing I need is 87 baskets full of chometzdik treats a month before Pesach…