Item Sets

Hello guys i was thinking about it a long time now Why are custom item sets so bad ? Not only you get random items even if you click the spesific map but also why can't you make it that way that to combination items with runes ? For example i want 2 make 2 different yi item sets 1 for hail of blades and 1 for conq but not only I get items from all the maps but also I can't get the item set i desire instead i get all items from both runes I think riot should work on that and upgrade item sets