Indeed. Very true. I think the trick here for those who do want to self drive is to try & avoid the park during South African school holiday periods which are different from those in the Northern Hemisphere as well as other peak times such as public holidays, weekends and most definitely over Xmas and Easter holidays. There have been times off peak season when I've seen hardly any vehicles.
The Northern part of the park will almost certainly have fewer day visitors than the Southern areas in part because of the distances and the prevailing slow speed limits.