Why making phone calls in EA still very costly

Making a call to China or America from Kenya is cheaper than calling within the East African Community (EAC), in spite of efforts to eliminate roaming charges and make phone calls cheaper through the One Network Area (ONA).

Calling within the EAC is so expensive that one would spend less per minute when placing a call to India from Kenya than to Tanzania or Burundi.
Burundi was the latest entrant in the ONA, joining Uganda, Kenya, Rwanda and South Sudan.