Madlock wanted a multi-year deal in an era when Cubs ownership and management didn’t really want to give those out. It was right at the dawn of free agency, which the Cubs didn’t really participate in either.
The Cubs offered Madlock a $110,000 contract for 1977, far below his market value. The New York Times reported:
Madlock wanted a multi year deal of at least 200K per.
So the Cubs traded him.