Games and stupid greed. Just look at Goma and Kivu province.
With the Chinese though, occasional fucking typical shite. Working in Angola years ago, we kept hearing that deal done to build new airport. We were waiting and waiting cause airport was shit. They finally broke ground. We celebrated. Building stopped and took 3 months before we found out from our connected Angolan friends what happened. Construction company told government the soil was great and would it be OK to ship to China. Took the Angolans couple months to figure out they'd found diamonds.
There's a new mine there now but thats why relations soured around 15 years ago. Took a while before big Chinese projects started there again.