Following the break up of the Soviet Union, there were plenty of aircraft and crews floating around looking for work. With a lower cost base and staff willing to accept pay and conditions below what a western operator would need to offer, there was no difficulty in undercutting established operators.
Corruption is not totally new in Russia and Africa or with some of those signing contracts. Once the correct backhanders are being paid the operation is left alone.
Overloading and breaking flight and duty time limits is taken for granted. Add in anything else you can think of; forged documentation, highly questionable maintenance, breaking minimums, flying under the influence of alcohol etc and the results aren’t surprising.
I’ve seen operations in Africa that in a first world country would have been instantly grounded and the people involved facing charges.