What is the reason for the active development of alternative energy in the 21st century?

It is difficult to predict how many more centuries or millennia humanity will survive, but it is quite possible to predict when oil, gas and coal will run out. Unfortunately, the bowels of our planet are not unlimited, which pushes the best minds of mankind to come up with alternative energy sources that do not end. Thus, for today man has mastered the energy of the Sun, wind, the force of the flow of water, ebb and flow, the inner heat of the planet. Energy production technologies are improving every day, which gives confidence in the prosperous existence of people in the future.