I have the same issue, but I haven't really seen fit to complain about it. It's free sales. All the skins there (or that could have potentially been there) will go on regular sale, so they aren't hampering your ability to get the skins you want in any way.
This is, and has always been, a ploy. Riot's goal here is to get people to buy skins that they otherwise wouldn't, so they make money even if they sell the skins at a "discount." That was always the plan. That's what the Snowdown Shop is.
And honestly, that's great! It's great for Riot and it's great for the community, in general! It isn't great for me, and it isn't great for you, and that's okay. We missed out on this deal, this time, because we're the kind of people that have more specific skin desires. I didn't expect Riot to adjust for that, and it's honestly not a problem. The resources to get a "better" algorithm would not have been worth the effort/money invested. Hard to blame them for that, isn't it?