Ratio of bill rate to salary of 2.5 to 3.5 is pretty typical in consulting companies. Billing has to cover lots of things, e.g. training, utilization, supervisors, sales, office, computers, accounting, etc. I expect they have particularly high overhead relative to the costs of labor in Africa.

Even onshore it's about going rate for most of the consulting firms. The 200% markup pays for holiday, sick pay, insurance, CPD, office space and time on the bench