Maybe Servais was just trying to give Karns some confidence by relieving him before a collapse: had he knew the bullpen was going to struggle even more than Karns did he sure wouldn't have changed, but when Karns goes out it's still a 1-0 game and if the bullpen hold the lead Karns gets out having rebounded nicely from a subpar game against Texas. It happened that the bullpen doesn't stop the walking and the bleeding but you don't know it when you make the call; Karns was coming of 10 walks in 8 innings and even if the Indians wasn't hitting him hard any lucky bounce was going to kill his game, his numbers and maybe even his confidence. Now Karns has the chance to be angry because he was removed too quickly and maybe it's better than being sorry for being relieved too late.
Just a little hypothesis, my view of the same game with a different idea.