1. Because if conversations in any type of story telling, but especially in fiction didn't give the reader/listener/watcher some type of insight, whether into plot, character, or timing, then it would be a worthless conversation. So, you want to watch a bunch of worthless conversations because of your interpretation of realism? I guess and I'm not saying you're necessarily wrong in regard to this specific show, but that would be some boring shit.
2. Spoiler -- if you haven't watched by now, then don't read. Because Claire Shaw (isn't that a terrible name) only has a temporary fix from Marty and still needs the Mexican product to continue offsetting expenditures to help her books. It does her no good to piss off an obviously very volatile personality in Javi so she gives him some information but not all of it. She can't risk permanent shutdown. She gives him enough to stay trustworthy enough but still gives the Byrds an opportunity to create or tweak a narrative they'll need to keep Javi supplying. And lastly, she's a little intimated by Javi and that was hinted at in the scene where she tells Wendy about meeting him in the garage.