Why is this not more famous?

John Wayne made many movies that were not westerns.

The film was made in 1962, when smoking was prevalent among both Americans and Europeans, especially the Germans and French, who are still big smokers. This was long before the war on smoking. Now they all drink wine. There was a lot of boozing too, common in a Wayne film and most "macho" films of the day.

By the standards of today, the business of capturing wild animals out of their natural habitat is considered cruel and inhumane. Businesses like the one in the movie are heavily restricted where they are allowed at all. Some people would abolish zoos if they could, even though Africa is very dangerous for animals now due to heavily armed poachers. There is a huge market in Asia for rhino horns. It is popularly believed in China that the horn of a rhino, ground into powder and consumed orally, acts as a powerful aphrodesiac. There is no scientific evidence to back this up.

Elephants are in danger for their ivory tusks. Attempts to abolish the ivory trade have failed. People still want ivory products. Drought has led to slaughtering thousands of animals for food. Besides that, Africa is very different today. It is full of violence, political unrest, and religious persecution.

Properly run and giving animals as much roaming space as possible, zoos and wildlife preserves are probably the last chance for the continued existence of Africa's once abundant wildlife. As it is, the West African black rhino is extinct in the wild and can only be found in zoos and preserves. Conservationists deliberately remove rhino horns and replace them with synthetic green ones to protect them from poachers while still allowing the rhino to protect itself and look for food, the function of their horns.

In short, this movie is not more famous, or rather, more popular, because it represents an Africa and an outlook on nature that is long gone.