Is Sagittarius A* a black hole at the center of the Milky Way Galaxy? What is the reason that galaxies seem to feature a centrally located black hole?

This is a correct interpretation of the existence of a black hole at the Galactic Center. The reason this is associated with the galactic architecture is because there is a need for a kind of seed energy in the creation of the galaxy at its point of origin. This represents a kind of push-pull phenomenon, that the act of creation creates a kind of void state and that will be present for a considerable interval, a kind of warp in the energy field of considerable magnitude because of the vast quantities of energy converted into physical appearing matter and other forms of energy. So it is, in one sense, a remnant and a relic of the galactic creation event. It has a powerful role to play energetically in further governing the energies brought forth. That is a complex discussion and will be a central mystery needing to be unraveled by cosmologists and astrophysicists working together.