(As a side-topic here, Leibniz wanted to posit something necessary, going by what we now call modal logic, but I think anything necessary in general falls back on what all possible worlds have in common, i.e. more or less just self-consistency.) — jorndoe

Interesting. This harkens back to the point I raised earlier about the immanence of the first cause throughout the whole. In modal metaphysics, if we take any event, we should be able to derive from it all the predicates of its subject. Tracing the lineage back, we eventually arrive at our reason.

You might also think of this in terms of duration, the rolling up of the past into the present. This gets taken up in the later process metaphysics so that the actual entities are causally connected to everything in the cosmos in an intensively connected system.

The existence of stable order (whether projected or existing as an objective reality) would suggest a ground which functions as a common root for all events. This would make the 'it all' a causal chain with a single origin. The original cause is immanent throughout the whole.
Without such a grounding principle, the existence (again real or imagined) of logical order is puzzling indeed.