I see where you are coming from but really you have to think of this from Chrono’s side, people would literally just accumulate the free currency and wait for a game they want, there would be less incentive to buy games from the site with real money. The company would make lose money as they pay for the keys and just give them away for free with no limit to the amount they would have to potentially give away every day. Even if Chrono are paying for the keys they put in the coin shop at the moment (which i don’t believe they do with a few exceptions, but don’t quote me on this) at least they are limited in the amount they give out and they get people to look at the daily deal with the potential of them buying it.
I am guessing the website is currently making more from daily sales then they are losing on the coin shop (otherwise they would likely stop the coin shop), but doing what you propose is fiscally irresponsible for them, the would surely go into the red. As you mention they showcase a good deal on a game every day which you have the opportunity to buy and that is the main focus of the site, the coin shop should really be thought of as a bonus.