9S also seems cool! And 9S also seems like he knows what he's doing! And 9S is perfectly willing to grapple with terrible questions like "the nature of morality" and "what it means to be alive" so 9S has also risen up in the ranks of people that Cole can ask questions to. It also helps that 9S is someone who's just rolled with Cole's everything like "okay! This is a thing!" and hasn't pressed/questioned him as much on some of his more esoteric points...because Cole's understood that as 9S understanding him pretty well to begin with.

also tell 2B you like her, holy shit, your mind has so much ust it's ridiculous.