It will come as no surprise that Summer in Southern Africa is HOT, and whilst WE all love a bit of Vitamin D, the animals aren't quite as fond (they don't have aircon) so they tend to tend to seek out the shade instead. The bush also gets most of its rainfall in Summer, so the foliage is far more dense - all in, the game viewing conditions are far from ideal.
Further South, the Cape battles with a persistent wind during Summer known as the "Cape Doctor" so we recommend visits in the 'shoulder season' months around April, plus later in the year in September / October. With fewer visitors you'll get much better value as well.