From the point and shoot cameras to the professional digital cameras, all have the feature “Auto ISO” and although one might have learned during a photography course how to use the manual ISO settings, one often goes just back to use Auto ISO. It’s just convenient.
And it might work in most of the situations, but not as well when being on a photographic safari. Photographing in the bush is different and the auto settings often fail to match the light conditions there. The Auto ISO often goes too high and the images look washed out. Use in normal bush bright daylight ISO 100 and you will be fine. But keep looking at the light and adjust the ISO manually when the light gets lower. You will see the results are much better. Depending on what manual setting you prefer, rather leave the ISO at 100 and play with the aperture.