There's some reason for them:
Ziggler needed someone to feud with until he cashes in MITB. Plus Jericho is gone the Raw after Summerslam, so they're making use of him.
Kane turned face by helping out AJ after Punk accidentally knocked her off the ring apron in his match with Bryan.
The rest, I'm guessing that they're too lazy to come up with an explanation, so they just turn them to see if they draw better as a face or heel.