Iron, specifically in the form of its isotope Iron-56, is the most stable nucleus possible, and thus the end point of stellar nucleosynthesis.
The binding energy of a nucleus, what causes the individual protons and neutrons to stick together, is different for different atoms. Using Einstein's formula for relativity, the energy that is no longer needed to tie the nucleons together is released as radiation. As the atoms increase in atomic mass, the energy needed to bind the atom changes its value, along the curve of binding energy. Past iron, adding more nucleons does not produce a more stable nucleus with excess energy, which is why the process ends at iron. And this is how stellar fusion occurs. A star at first burns hydrogen to make helium, and then after some time, in larger stars, to make carbon and heavier elements. An atom of iron-56 is 6% less massive than its component nuuclei, but because of the great difference between matter and energy, that 6% is enough to provide tremendous amounts of energy.
If stars were perfectly efficient engines, there would be a lot more iron in the universe, since it represents the end product of energy formation. However, the energy of activation needed to merge lighter nuclei is quite a bit, and is only available in large, dense, hot stars nearing the very end of their lifespans. Even in these stars, the process is not totally efficient, because as the star goes through its life, especially its final throes, much of its mass is ejected in the form of lighter elements. And when the star does undergo its final collapse, much of the heavier material, including the iron that was built up so painstakingly, is drawn down into the remnant, be it white dwarf, neutron star or black hole. This is a somewhat disappointing move, since that rare iron will not actually be of use by the rest of the universe. And yet, stars are massive things, especially stars that go supernova, so even if only a small percentage of their mass is converted to iron and ejected, it is enough to seed the universe with much iron.
And that is why a good part of the earth's crust and many of the other rocky bodies we can observe are made of iron. Even though iron is a heavy element, and must be made in a series of complicated steps under very extreme conditions, it is the end of the line for stellar nucleosynthesis, and thus is more abundant in the universe than could be guessed. Over time, more iron should appear, and theoretically all of the hydrogen and helium in the universe will be turned to iron. Of course, stars are inefficient, and even in the distant future, there will still be diffuse clouds of lighter gases floating around, but there will definitely be more iron.
And this is the long story of why a common element here on earth, and one that is necessary for our industry and other endeavors, is here because a combination of somewhat mysterious laws of physics, and the efforts of the most extreme stellar furnaces.