The "immoral mining laws" are a legacy of former times.  They were then imposed, initially in the diamond mining area, to counter the problem of mine workers stealing stones from their employers. (The parallels in the gold area are a little more difficult to imagine.)   In addition, they help (should help, at least) in the collection of taxation from the independent "artisanal" miners. (Tax evasion by the zama-zamas, and their sponsors is a major current talking point: large mining corporates are pretty compliant in their accounting systems, in spite of widespread accusations to the contrary.)
How to bring all players together is still a major problem, without introducing totally ineffectual bureaucracy in the process.