.Well, here on EN server, the only Quick Rune you can redeem from Exchange Shop is the Purple Quick Rune .. Yellow Quick Rune is only obtainable from the Recharge Rebate Event at the Max Rebate .. Red is not yet available in EN as far as i know and i only saw that Red Quick Rune on one of the videos of Memo, where he got an Optional Pack that contains Breakthrough Pill and Red Quick Rune, he got it for recharging 100k ingots ..

Possibly because of the Worth of the items .. Big Spenders will keep spending till they get 4 pcs of it and that means income .. Or in nicest way, it is one of the pros of being a p2w .. simple as that ..