There's no god, the answer is something way way way bigger than our brains could ever hope to understand.  There are infinite reasons why infinite universes exist, have existed, and will exist.  Trying to look for a simple answer is human nature; there is no answer.

Logic is a predicate for truth.  Truth takes the form of sound, rational statements (note: root word of 'rationale' is 'ratio').  Truth, as it is relevant to us, does not exist outside of these rational statements.  Accordingly, truth should be modeled in terms of the mind as it relates to the rest of reality.

The best model one can theoretically come up with to explain something must meet a few criteria:  It must 1) Be internally consistent, 2) Comprehensively and soundly explain all information it attempts to do so, and 3) Introduce the fewest number of assumptions, ideally zero.  Falsification of the model can happen on two levels.  At a lower level, the model can be rendered internally invalid if new information is introduced which should be explained by it, but isn't.  At a higher level, the model can be rendered externally invalid if another model, which is broader in its scope, not only explains all information in the original model, but synthesizes this knowledge with other information unexplained by the original model (the result being a deeper understanding which predicates any topological understanding).