Depends on the available material during the formation of the solar system, and the dynamics in play at the time. Our system appeared to have a single main concentration of matter that then became the sun as it hoovered up most of the matter around it. Other systems might have had multiple concentrations, resulting in a number of such massive objects. If there were two then you might end up with a binary system. If there were three then it is likely that one got thrown out of the system by the gravitational dynamics of the three-body system, resulting in a stable pair.
