SAI_Peregrinus parent
Workaround I've experienced in practice: some stores only allow purchasing gift cards with cash. This doesn't allow online-only gift card purchases, so it's not a full solution, just a workaround.
Another way gift cards have been used is as a means of transferring "wealth" to anonymous scammers.
Dumb people were being scammed in Singapore, until the financial regulator here clamped down on gift cards altogether. It used to be trivial to buy Apple, Google, and Steam gift cards in Singapore convenience stores. They're no longer being sold anywhere.
I'm not sure how requiring gift cards to be bought with cash would help prevent that