This isn't a cutthroat business like that. Relationships, even with opponents, matter.

Say you're Atlanta and you want to send a scout to Cleveland to check out a player whose contract is running up. If you have a good relationship with the Cavs, you get a good seat for free in the press section and a media pass so the scout can come in during warm-up and everything and have access to the event level.

Speaking of warm-up, say you pull the trick you were talking about pulling, now Cleveland tells your guys to fuck off when they come to town and they make your guys do their warm up at some shitty high school gym instead of a nice court with decent facilities. Now your players are pissed too.

Now say you get fired, like all GMs eventually do. Friends and colleagues of the guys you fucked over by talking about a negotiation with other teams are now not going to ever recommend you be hired by another team. You're black listed. All for what? Is Atlanta gunning for a ring this year? No way. None of it would be worth it.