The cards are nice for people who you are not going to give to anyway or ppl who wouldn’t have a use for your shalach manot. For example if you are giving someone on a special diet or a diabetic than a card is much more appreciated than food they cant eat. But, I always think it is nice to give back to someone who comes to bring to you. If someone spends a lot of $ bringing you a nice shalach manot and you give them a card which costs $1 it can be a little insulting. Also, because ppl can give cards to 500 ppl it does insinuate (as a pp said) that you are not of their closer friends.
On the other, the situation has gotten so out of hand where so much is expected and ppl are expecting from all their friends and acquaitances in the city.
Giving simpler shalach manot is often one solution. You dont need to spend 10$ on each. Just something cute to spread friendship and say I was thinking about you.