Because you don't make personnel decisions based on 20 innings of work. Or ERA rather than FIP or WHIP, not that he looks good there. But either way, you look at what he's done for the last 3-5 seasons overall and then decide whether he's cooked or just having a bad year. Given his age and salary I'd probably cut him loose.
Of course, while I believe the epic nature of this bullpen's failure is largely a matter of luck/random chance, you also can't say it's a coincidence if almost every player is experiencing the same problems. If the bullpen fails no matter who is pitching you also have to look at the rotation, the defense and the coaching staff. And then it all comes back to the GM obviously.
Unfortunate they couldn't cash in more runs and Bohm got thrown out. But Harper's AB was even more unfortunate. He got hurt too?
