The sky is blue, the grass is green and GTA V is on sale. A different platform and different retailer, but discounted nonetheless. These sales are being handed out like candy as retailers know for a fact that GTA V sells really well when the price is slashed a tad. Of course it sells really well at full price too, since, you know, it's GTA V.
We're talking about a game that has sold over 60 million copies and rates are only going up. This is a three year old game outselling the newest AAA massively hyped releases consistently. Hell, the game's soundtrack is bringing in massive profit.

Next in line for the daily discount duty is one of, if not the largest online store fronts in the world. Amazon ships everything everywhere, has been around for two decades and has an ever growing customer base. They stock every version of GTA V be it physical or digital, along with all available Shark Cards.