Ground staff Lying

I flew Cape Town to JHB and back on the 4th and 6th of May respectively. At both occurrences at check in I requested exit row seats mid plane for my wife, mother and I. Both occasions I was informed that the plane is fully populated and no exit rows are available. The flight to Cape Town only had about 60 passengers and all 12 exit rows where open. The flight back to Johannesburg again was not completely full with 6 exit rows mid plane open. This leads me to believe one of two things