Original: It was chosen to replace the mainland town of Bata as the capital of the country in 1969, and was renamed Malabo in 1973 as part of President Francisco Macías Nguema's campaign to replace European place names with "authentic" African ones.
Simplified: The city was renamed Malabo in 1973 because President Francisco Macías Nguema wanted to replace European place names with "authentic" African ones.