Basically the title of the post... Sprites were added when Sleep was gone, Slooms got added back with a reworked Sleep status, and Sprites were never updated to have a resist.
Easiest thing to do is make it so that you get the Sleep Resist perk along with the Curse Resist perk. Both are some of the rarest statuses in the game, so having two perks for that level would be fine.
We technically already have Curse resist as "Purity", but I agree we need Sleep resist. I wish we could equip three other passives, those three slots have been sitting empty for sprites for so long and would love to equip more bonuses to them.