Why are two objects with mass drawn to each other?

The "why" is sort of tricky. You can think of every mass exerting a force on every other mass. According to General Relativity, a mass will actually distort spacetime in its surroundings, in such a way that this affects other masses.For more details on what we know and what we don't know, you may want to look up "Gravity" in Wikipedia, for example.