I would love to build the more unique items

There just isn't any room for them. Outside of supports ad support style junglers, who have at least three slots taken from just being a support (Boots, Sightstone and suppot item/ jungle item), no other role really has the room to build these. Ohmwrecker, for example, has stats for a tank but for similar gold you could build a item that gives more. Just like still only having six bans more and more stuff is introduced and there just isn't room.