‘Private Practice’ showrunners exit series

it seems that alot of abc shows have lost their showrunners in the past 6 months. flash forward, v, lost, private practice,
grey\'s anatomy, scrubs to name a few. i know there are a lot more, but these are the shows that i find most annoying. is it
any wonder that people from these shows are either jumping ship before it sinks or are getting fired for doing a very poor
job on these shows.