Because most of Namibia is the Namib Desert and the Kalahari Desert.
Namibia is 25% larger than Texas or France and has barely 3 million people. With 500000 in Windhoek, the capital and 200000 split between the coastal cities of Walvis Bay and Swakopmund, the rest is scattered in small and mid size towns and settlements.
There are way more people in either Johannesburg metro area or Cape Town metro area than the entirety of Namibia and most of it is because of Namibia’s landscape.
The Skeleton Coast extends for 500 kms North of Swakopmund and Walvis Bay to almost the Angolan border and hardly any big cities there except small towns and settlements between Walvis Bay and Cape Cross Seal Colony and barely anything north of it.
Namibia is an amazingly beautiful country and the lack of population is what makes it so beautiful. Lots of wildlife in the desert and along the coast.
Daily life… well, it goes on. Namibia can get really cold in the winter without snowfall and vast open desert cools fast at night and winds rip through the desert with little to no barriers so do not underestimate the winter in Namibia in the desert regions and elsewhere as well. Namibia is a reasonably developed country and exactly the opposite of being in countries like India where there are people everywhere. Namibia is so vast and so sparsely populated and you feel really small among the vast landscape.
South Africa has a much varied and friendly landscape for human population centres and considerably big cities in Cape Town, Jozi, Durban, Port Elizabeth and lots of cities along the Eastern and Western Cape coast and the Garden Route . There are quite a lot of population centres in SA especially in Eastern and Western Cape, Gauteng ( where Jozi and Pretoria are), KwaZulu Natal and the rest of the provinces have a fair bit of population as well.. I think except for Northern Cape which is a sparsely populated province, almost all other provinces by themselves have more people than the entirety of Namibia.