Conversation so far:
What did Zheng do in China?
Imperial officials minimized the importance of Zheng He and his expeditions throughout the many regnal and dynastic histories they compiled.
why did they say he was not important?
State-sponsored Ming naval efforts declined dramatically after Zheng's voyages.

Question: why did it decline?
Self-contained rewrite: why did Ming naval efforts decline after Zheng's voyages?