Where does your experience come from? It seems appallingly out of touch.
When Apple, Amazon, etc, seek to have retailers carry their gift cards, the retailer needs to have an incentive. So the gift cards are usually sold for below face value to the retailer. In turn, some retailers will sell gift cards for below their face value.
So, e.g., at this moment, Nintendo eShop $50 cards are $44.99; XBox/Sony Playstation $100 gift cards are $89.99; a $500 gift card on Alaska Airlines is $449.99; $100 at Hulu is $89.99.
These are not particularly good prices. Oftentimes Apple $100 gift cards will be $79.99.
The other incentives at Costco still hold, too; you can get the Executive Membership 2% back and the 2% credit card cash back.
Where gift cards are available, they are never cheaper than face value due to basic market dynamics.
In retail stores in non-Western countries I have never seen a gift card with e.g. 100 unit value sold for less than 100 units either, although I haven’t specifically looked for such.
In degenerate cases, I can see that the reverse could be true.
In this thread, a fundamental misunderstanding of how gift card market works seems to prevail.
There’s basic arbitrage. Vendor Acme in region X locks out people from region Y (e.g., based on payment method address); Alice lives in region X and can buy an N value Acme gift card for N-1 at a local store; Bob lives in region Y and wants to transact with Acme; Alice buys a gift card for N-1 and sells it to Bob for N+1 online; Bob gains the ability to transact with Acme, Alice gains 2 as revenue.
Thus, gift cards going for higher than face value does not automatically imply anything beyond a market acting as it should and is not specific to Amazon in any way.
You... are aware that the primary market for USD-denominated gift cards is US residents, right?
Gift cards are always cheaper than face value. The basic economics tells you they can't be more expensive than that, since they are similar to money, but worse. They can easily be cheaper; $300 at Starbucks is not as good as $200 wherever you want.
Your incredulity is pretty shocking; if you want to see gift cards sold cheaper than face value, all you need to do is walk into a Costco.