Meh.

Sales such as you are expecting exist in the Real World because shops want to clear out old inventory that is not selling as well for new inventory.

Digital sales hold no such problem. And the length of time something has been in the shop (SD Fenrir specifically) has no bearing on its current price, or its discounted sales price.

Your Free-to-Play shop, on the other hand, has to be as inexpensive as possible in order to entice players to continue to pay money for items they don't actually need (unless it is actually a Pay-to-Win shop). Most of those shops make their money on selling you 'keys' to unlock boxes in-game to, possibly, maybe, sorta, kinda win a useful item.

Any income is good income for the F2P industry. Sales run whenever the game income appears to be dropping, as the F2P shops need you to put in an order to continue running, which is the reason you think you get 'better deals' there.