Amazon Prime Video is able to remove a video from your library after purchase.
We are contacting you regarding a past Prime Video purchase(s). The below content is no longer playable on Prime Video.
In an effort to compensate you for the inconvenience, we have applied a £5.99 Amazon Gift Card to your account. The Gift Card amount is equal to the amount you paid for the Prime Video purchase(s). To apologize for the inconvenience, we've also added an Amazon Gift Certificate of £5 to your account. Your Gift Card balance will be automatically applied to your next eligible order. You can view your balance and usage history in Your Account here:
Okay, so go buy a gas station sandwich for that money. You weren't paid anything, you got "store credit in gift cards". Which means you paid them for a movie, they took your money, then later they "gave you back" something that doesn't have any value at all to them - they can "print" store credit anytime they want, and those small amounts won't matter in the long run.
Fine, but that is how it works pratically everywhere, it is not an Amazon specific thing.
It is extremely rare that even a real store give you back real money if you return something and some time have passed, they usually just give you a coupon of the same value.
The problem here is that Amazon take your item, not that you return something and got a coupon for it instead of real money