ABC wanted more westerns from Disney during the later 50s, which brought out a lot of "Frontierland" mini-series like Elfego Baca and The Swamp Fox. This was one of the reasons Walt fled to NBC, the other being that NBC had the technology to broadcast in color, while ABC could only broadcast in black and white.
While the show was doing good on CBS, Disney didn't let the show go on after the 1982-83 season so there wouldn't be any competition with the new Disney Channel.
Or, at least, personal recognition. This series was most people's introduction to Walt as a person rather than just a name above the film title.
Fess Parker became forever associated with the role of Davy Crockett.
What Could Have Been: The producers and director of the 1997 Wonderful World of Disney remake of Cinderella planned to follow it up with an adaptation of The Wiz. They signed on Paula Abdul to choreograph, and the then-unknown Anika Noni Rose (who'd later star in Disney's The Princess and the Frog) to portray Dorothy Gale. However, rights issues with Universal, the studio that distributed the 1978 movie version of The Wiz, prevented The Wonderful World of Disney from progressing much further with their take. In 2015, the producers finally did release a TV version of The Wiz, but for NBC instead of ABC, and with a different director (Kenny Leon), choreographer (Fatima Robinson), and Dorothy (Shanice Williams).