By listing protection of the natural world in a constitution or other foundational document, a country sets up a strong stance for making sure the environment is protected. This type of foundation would ensure that future laws were not made that could hurt environment. If the environment is destroyed, everyone suffers so stating its protection as part of the very foundation of your government is a good idea.
Namibia is a beautiful country, and the inclusion of protecting nature in its constitution might be a big reason for this. Humans are selfish by nature, and it is hard for us to think about future generations of life on Earth. However, we need to think about them. If we don't work a lot harder to protect our planet and stop destroying it, the planet may be uninhabitable for future generations.
Countries tend to think of themselves in terms of territory, population, and resources. Resources are usually whatever is naturally available that humans can use for industry and this is flawed thinking. Resources are not what you can pull from the land and sea, but the land and sea themselves. By affecting various parts of the landscape and ecosystems, we cause lasting change and damage that could potentially make livable areas uninhabitable, for ourselves and other types of biological life, in the long term. This is not to say that every country should stop what they're doing and make massive change to prevent climate change or what-have-you, but that countries should continue forward with progress, improvement, and respect for the world that houses us.
Yes, more countries need to adopt this stance because it is the only way we will be able to combat global warming. Too many countries choose profit over nature, and we are losing some of our most valuable species. The health of the world is critical to our survival, and everyone should get on board.
Many countries of the world are trying to protect the nature. Those who cares about nature already have laws as are protecting nature. It won't change anything except for that whose who stand for nature will get a fuzzy feeling. What is the point of making new laws as will not change anything