Why Moria?

[Tuor in Gondolin]

About arguments against heading west from Rivendell:
As it turned out the path might well have been clear if
the Fellowship had left immediately after the Council,
certainly Nazgul would have been a nonfactor, as was
quickly established (by a high probability) at the Council,
and I question using months to push that probability up
a bit by searching far to the north, south, and east, as
Aragorn etc. did- as opposed to leaving right away.

The point of encountering different cultures is a good one.
I've thought of it and it seems JRRT could have rearranged
things to cover almost all (for example, relocating Lorien
to an area in Andrast), then having the Fellowship attacked
and splitting up, the three walkers chasing orcs and Merry and
Pippin while Sam and Frodo go across south Gondor,
receiving aid from Imrahil (including crossing the Anduin).
This would still allow Aragorn's involvement in Rohan and going
on the Paths of the Dead and give Imrahil a much more
interesting/complex situation. However, it doesn't seem to
realistically allow for a direct (even if relocated) Moria
involvement. You'd probably have to cram too much into one area.

The overall point of water travel in a preindustrial age is that
it is much faster (and if deep ocean travel is avoided) generally
much safer then land travel, and coastal travel, at least to the
Andrast, would seem to fulfill those requirements.