There is always funny player who refuse to get morellonomicon in ARAM, why?

the other team's got + the other team's support got and our AP refused to get and instead early game rush ... In the last fight before we lost, after our brave evaporated half of the HP of ,our funny went in, and use all his abilities on . And then, the literally regained full health plus bloodthirster's shield by just autoattacking the and his hallucination.... I really do not understand that in ARAM, why so many people refuse to build when the other team clearly stacking healings...