 The gravy train was moving fast and he didn't turn anything down. Many times, if a new band was going into the studio, the producer would still use these session musicians. They usually weren't allowed to play on the album because studio time was expensive and the producers had to make sure that they could get in and get out with the recording. Now, recording technology in the early 60s didn't allow for mistakes. If you had 10 to 15 players in a room, they all had to nail their parts. There were no computers helping you punch in.