What happened to champions getting new skins roughly a year after their release?

Since Illaoi, heres the metrics on what skins have been released for her and every champion after her.

- 0 (Nearly 2 years since her release) - 2 - 0 (over a year since his release) - 0 (over a year since her release) - 0 (over a year since their release)

??? Like I remember when the 2014 champs got their skins consistently in 2015. What gives with this year?