He froze himself out. He was credited with writing eight of eleven songs on The Piper at the Gates of Dawn, with shared credit on two more. On A Suacerful of Secrets, he was credited with writing only one song, the short (3:00) Jugband Blues. This wasn't because of any effort by the others to exclude him, or limit his participation. He was so fried on psychedelics by then that they could not rely on him any longer, either for creative input or live performances. They've described their decision to move on without him after the second studio album as a sad, but necessary step. They said they missed the charming, witty, creative mad genius they'd known in the earliest days of the band, but that person was no longer available.