This may be a dumb qeustion but have you tried drawing before you press the rob button? IIRC, you have the option to do so and if I had to guess, I'd say 1 in every 10 people robbed me as not everyone is armed or people were scared because I pulled out premature rather than later.
Robbing people in Red Dead Redemption 2 seems impossible. Every time I press the "rob" button, the person just draws on me and I have to kill them.
I am seriously missing playing RDR2 though, unfortunately I uninstalled the game after I finished so no clue but I'm guessing that since I'm not a PS+ member, my save is gone. Oh well. The game is pretty much open from the second chapter anyways so no huge loss.