Why Moria?

[alatar]

Originally Posted by Rhod the Red

Improvise. He said something near the Redhorn Gate passage like "Let's plan only as we progress".

Exactly. I think that there may have been three determinants affecting the planning. One, not knowing exactly what they would find around any bend of the road, the FotR had to assess the path as far as they could foresee at that time. Like the crossing of the mountains - that was the plan until the snow and giants/boulders changed everything. Two, there were certain sanctuaries that were to be visited after some traumatic adventure (i.e. Old Forest -> Bombadil; Riders -> Rivendell; Moria -> Lothlorien; Black Gate -> Ithilien) in order to replenish the body and soul for the next stage/level of the journey(s). And third and to me most important, we mustn't leave out that seemingly infallible guide *stupidity*.

Think about it. It's stupidity that keeps Frodo from being found by the Black Riders, it's stupidity that gets Merry and Pippin into the hands of the Uruks, ultimately leading to the overthrowing of Saruman. It's the same idiocy that allows Aragorn to get Sauron to play his hand earlier than he may have wanted (i.e. Pip looking into the palantir), and where would Middle Earth be if Gollum chose to leave Sammath Naur before dancing a gig?

I'll leave the other examples to you to find.