re "was just curious as to why no one ever overlands in something like a Ford F-150 or Ram 3500 in Africa"
A key concern overlanding anywhere is whether you will be able to find spares, whether for routine maintenance or for unscheduled repairs. Ford doesn't sell the F150 in Africa as far as I know, and Dodge is no longer selling anything. This is a generalisation, I realise, however I am fairly certain that you won't find either for sale in Namibia or Botswana. I don't think many, if any, were ever sold (I did drive an F150 many years ago in Botswana - brought in for a specific project, and I suspect that it was the only one in the country. We did our own maintenance - there were no dealers at all). So, you won't find parts, mechanics won't be familiar with maintenance or repair, and if you ship one of these in, you'll need spares and skill to do it yourself. If you break something you haven't brought with you, it may be weeks (or never) to get a replacement.
I've seen a few big North American vehicles in Africa, usually either waiting for spares, or abandoned when fixing them was impossible, or simply too much trouble. About the only North American vehicle I have seen in Africa is the Jeep, and they are few and far between outside cities. It just makes more sense to travel in something for which spares are (more) readily available, and with which mechanics are familiar.