Sir Mugo never encountered other sacrifices, as soon as they arrived at the mannor, Jerk mugo, which had the most power over the body, would have sex with the sacrifices and then monster mugo would arise with hunger and eat the sacrifice. This didn't happen to MC bc he brought cake, bringing out Sir Mugo, who have him his blood, stopping the other mugos from physically hurting him.
I'm pretty sure it's because the faster the sacrifice dies, the faster another one is sent (every 12 years) and he wants to slowly kill everybody in the clan. Now his objective has changed, he'll take way longer to do the sacrifice or just not do it at all, that way, the kang family will have to wait many more decades to get a new wish and renew their power (also why they were trying to kill jaheon) and Jerk Mugo also realized that the kang family doesn't give a shit about the well being of sacrifices

wait i’m confused did mugo ever sleep with any of the other sacrifices ? i thought he didn’t but the old mugo keeps saying jerk mugo is characterized by lust so was he always full of lust or did he just gain lust when he met ja heon ?