Simple.
Western envoys - liberal democracies always concerned about foreign and internal affairs of others. Not amazingly NASA and Jubilee took the opposite contra positions on the interference a short while ago, 2013.
China - never bothered about the internal affairs of other countries - which is self serving as they reject any interference in cross-strait politics with Taiwan. So long as business keeps flowing that is. The CCP and Jubilee are in close dialogue on structures, policies, etc - complete with a Jubilee Party CS!
African envoys - no political, moral nor economic authority to interfere. What exactly would the RSA or Nigerian envoy say to Uhuru? Shouldn't their own focus on Zuma's scandals or Boko Haram first? They have no excellence to share.