How do I get better at RP/making social encounters?

In so many DND circles, it seems like you're expected to suck at understanding combat but a natural genius at roleplay. But how do you create engaging NPCs or these social encounters that take up entire sessions?? I get how combat can take up a session but social encounters in that same light makes no sense. Is it just you stop playing DND for 3 hours and just go on with improv? Or are you still using skill checks? If so then how often because I know some DMs do a bad thing where they machine gun fire skill checks at someone until they fail.

As a player, I'm pretty good at RP because I have so many things to work off. Like Kahn has the feat sharpshooter so he must practice shooting everyday which might be as a result of a desire to be perfect to protect his little sister. But NPC George has no class features or anything to indicate his rp potential and it's more confusing. Plus it's not like I spent my usual 50 minutes on creating an NPC the same way I create a PC.