why does the legendary skin (rp1820) is not on sale like the (rp1350->975) when first released?

to clarify the question: Why do the legendary skins (worth 1820 RP) never go on sale while lower-priced skins do?

Also, the ultimate skins are a relatively new thing to the store and are released very rarely/cost a lot more than other skins so RIOT generally promotes the skin to active players by having a sale at half price before the price goes back to its permanent value at 3250(?).

I believe the legendary skins don't go on sale to make them feel more...well "legendary" since they're considered skins that are above and beyond the normal ones in terms of textures/animations/changing the feel of playing the character.