I feel that when giving a reason why someone did not redeem a key offered, there could be more than just a few tick box options. My personal reason for this is that I am handicapped with sight and I am also epileptic. Both of which limit my chances of playing certain kinds of games.
I think it would help the devs if it was possible to, say, write a small info blurb or something of what the reason for declining was. In my case the reason could simply be that, say, the game had too many flashing lights. This is just not possible with the current system.
This might be more of a niche thing but personally I think it could give better info to the devs about why someone did not redeem a key if it was possible to do more than just tick a box.