It had to adapt to an environment that did not give it organic matter to survive. So it learned to take the energy from hydrogen gas to convert inorganic matter to protein and fats. Other microbes have a much slower metabolism so they can survive in an environment that does not have much nutrients. In places where there is a scarcity of space, microbes will not reproduce. In reproducing they would actually be destroying themselves because of the lack of space and possible nutrients.
Nutrients are essential to life.
If the microbes are to survive they must have these nutrients. Microbes, like all life forms, adapt to their environment so that they may survive. Temperature is another factor that microbes and all life forms adapt to. We humans have a certain temperature range that we can exist in. The microbes have their temperature range.