Why does Decker want to retire the six andys that Holden was unable to

Deckard is good at his job. Rick hates his electric sheep precisely because he believes it cannot feel any love for him, even though he cares for it. This feeling allows Rick to perform his work as a bounty hunter because he believes that androids, like his sheep, are incapable of true human emotion and therefore not worthy of life in a society in which life is the highest ideal.