McCarver was a very good catcher. But was traded by the Cards to the Phillies in the infamous Curt Flood trade.
October 7, 1969: Traded by the St. Louis Cardinals with Byron Browne, Curt Flood and Joe Hoerner to the Philadelphia Phillies for Dick Allen, Jerry Johnson and Cookie Rojas. Curt Flood refused to report to his new team. The St. Louis Cardinals sent Willie Montanez (April 8, 1970) and Jim Browning (minors) (August 30, 1970) to the Philadelphia Phillies to complete the trade.
August Busch had back-to-back World Series teams in 1967 - 1968. He proceeded to dismantle the team, trading away Jerry Reuss and Steve Carlton among others. Imagine what that team would have been with those two. McCarver was traded mainly because they had Ted Simmons coming up.