When supply exceeds demand, retailers generally rely on maintaining competitive prices to ensure that other retailers don't secure more sales. In a way, they are somewhat desperate for cards to sell. While, in the current state of the market, it is still true that lower prices are favored by buyers, the need for a retailer to set a price in the ballpark of the MSRP is greatly reduced because they can be confident that enough sales can be secured to deplete their available stock at higher prices, since competition between buyers is much more significant than competition between retailers when demand greatly exceeds supply. (The question becomes "Why should they sell to you?" rather than "Why should you buy from them?")


Keep in mind that production of GPUs and graphics cards was originally designed for a market where the average user has 1-2 desktop PCs, each with 0, 1, maybe 2 discrete graphics cards each (3-4 way SLI/crossfire are uncommon, due to the diminishing returns offered and generally poor support overall). Average users are expected to upgrade their graphics cards no more than once per new generation of GPUs, often much less frequently, and some users purchase prebuilt gaming systems.

Of course, production under that model always maintained a surplus, since you could always purchase a recent graphics card at or below MSRP at almost any time.

Now, increase the popularity of mining:

A typical mining rig has somewhere on the order of 6-12 cards, to balance out the desire for squeezing the most of the purchase of one rig base (motherboard/CPU/storage device/memory/etc.), and avoiding having too many eggs in one basket + setup headaches. Even if just 1% of the knowledgeable PC-building community were to average 3-4 rigs each, demand would increase from the previous model significantly, likely far beyond the aforementioned surplus of cards. (After all, maintaining a ridiculously large surplus of cards would be a huge waste, so there was no reason AMD/Nvidia and their card manufacturing partners would constantly be prepared for huge increases in demand.)


Regardless of what Nvidia might tell its partners about favoring gamers over miners, a seller gets paid the same amount regardless of what the buyer chooses to do with the card (neglecting warranty services). If sellers strategically set prices just below the threshold at which mining appears* to be unlikely, then the inflated price allows the seller to receive the greatest revenue from their limited stock.

*The appearance of the threshold is more important than what it may be in reality, since uninformed buyers may attempt to purchase cards at absurd prices, if they choose to believe that they will achieve a significant return on their investment before their hardware becomes obsolete.