Riot's Choices for Skin Sales

I think that it's obvious that many players in LoL use the skin sales predictions chart, but if you don't know what it is - there's the link.

The reason why it is used is so people can expect when their favorite skins will be on sale, so they waste their RP. Yet, what baffles me is that for some reason Riot doesn't work like that.

For instance, Project: Leona, one of my personal favorite skins, hasn't been on sale for about 700 days (about 2 years) - from its launch date. In the meanwhile, skins that haven't been on sale for about 400 days (for example, Guardian of the Sands Xerath) are, or will be in the next month.

For me, it's just very weird because you can clearly see the ~year gap between the last time both of these skins were on sale, yet Riot still chooses the ones who have been more lately for their sales schedule. And it sucks - because I know that I'm not the only one who waits for these skins to come out on sale, and every month that passes and you see the sale schedule, it's just disappointment after disappointment.

Thank you for reading :)