The are few reasons why people are looking for GC that:
1. amazon credit card can be linked to 1 Amazon account only and some people use Amazon GC at multiple accounts
2. If amazon suspend the Account where credit card linked to, you can not apply it to another Amazon account
3. amazon credit card is available for US residents only and GC can be used by international shoppers
4. Not everyone can qualify to amazon credit card due to low credit score or other reasons
5. Some need more Amazon GC than amazon credit card limits
Maybe more reasons that I can't think of now
Yes, factoring in you want to use multiple accounts and that you might not qualify for the credit card then those are some solid reasons.
But with an ink or other cards, no need to lay out cash on the spot!
And the PITN everytime sending someone money whether TD/ Chase or any other account while using quick pay/send money, account gets suspended or stuck for sending multiple payments to new users/recipients.