Declining ratings
Good Luck Charlie's ratings had been declining since its third season. In the fourth season, the show's average viewership was down by about 25% from the previous season. This decline may have been due to a number of factors, including the increasing competition from other children's programming and the changing viewing habits of children.
High cost of production
Producing a television show is a very expensive undertaking. The cost of producing Good Luck Charlie was likely quite high, due to the large cast, the elaborate sets, and the use of special effects. The network may have decided that it was no longer cost-effective to produce new episodes of the show.
Desire to focus on other projects
Disney Channel is constantly developing new projects, and the network may have decided that it was time to focus on other shows. The network has a number of new projects in the works, including several new live-action comedies and animated series.
In conclusion, there are a number of factors that may have contributed to Disney Channel's decision to end Good Luck Charlie after its fourth season. Declining ratings, the high cost of production, and the desire to focus on other projects were likely all factors in the decision.