Think of it like coupons vs. promotional gift cards given out by a grocery store. They use coupons in a situation where they want to encourage you to do something (buy X product), but want to limit the cost to themselves—the maximum discount is 100%. This is analogous to a non-refundable credit.

With a gift card giveaway, they’re saying the situation is such that they want to give you more money to spend, because that’d be better for everyone. This would be analogous to a refundable tax credit, which is mostly aimed a people with lower income, because helping them make ends meet and maybe even have a little extra to spend is better for everyone in the grand scheme of things.