Because it is not constant.
That means that humans might use solar energy instead of fossil fuel.
I'm not expert, but I might say that other, better, energy sources were not around at the time when they choose there main energy source.
your life will be less movement...
It might get enough energy for its needs, or it might not.Note that this is the usual situation - there are usually other organisms, with which an organism has to compete.
hi
Biomass
If you had a sufficiently cheap source of those two chemicals you might very well want to use them as an energy source, but as it is, you would use more energy to manufacture the HCl and the NaOH than you would get back by using them as an energy source.
Currently we rely on nonrenewable energy sources for fuel. When these fuel reserves run out, in theory we run out of energy. A second approach to your question might be that of pollution. Primary forms of energy have proven highly pollutive.
Heavy water contains heavy hydrogen, i.e., deuterium. Once nuclear fusion is improved, it might become a viable energy source.
I had to find an alternate solution. When you alternate between two opinions, people might think you are indecisive.
Other sources of energy that will not run out are tidal energy, from the rise and fall of Earth's ocean.
The Gulf countries would become very poor.