Because Lothar is destroyed by Soa and Sob, the last thing a Rescue deck needs. Cliff has lower power, is more vulnerable to Sob, Soa and pretty much every clan. It's Survivor not Deathmatch there's no need for the extra damage, it's about winning with fewer pills, Hence why he has used Sledg.
Perhaps your correct Mr Intelijent I just can't rely on such low power even if it does get Revenge Soa after it, it's just not good enough when your left with 8 - 10 pillz because you just can't play stupid anymore. Sledg destroys those Pirates, and Lothar is just a highly unstable card in survivor, I don't get why someone would even consider him there.