When Voyager is taken into fluidic space against its will in Scorpion Part II, why didn't the intense density of matter instantly crush the ship?
There could be numerous reasons Voyager wasn't immediately crushed when it was translated into the Fluidic Space dimension. The primary problem is we are assuming Fluidic Space behaves like water does on our world in our Universe. One of the only things we can be certain of was Warp Drive would not function there and ship speeds were limited due to the density of the Fluid.
I suspect that we may never know the "real in universe" answer since I'm not sure there is one (the out of universe answer is pretty obvious), however I've been thinking about this and here are my thoughts.
Water pressure on earth is due to gravity pulling the water down. In our universe if you had a large area of space filled with fluid, it's gravity would eventually cause the liquid to collapse in on itself into a sphere. This is sort of how planets formed in our universe - clouds of dust in space slowly collapse down into dense spheres we call planets.
Since this doesn't happen, my conclusion is that either gravity works differently in fluidic space, or the fluid has no mass. Either of those would also explain the lack of high pressure on Voyager's hull. This also explains why Voyager seemed to indicate no planets, stars, or other objects in space. Planets and stars are formed by the gravitational attraction of matter in space. If for some reason that matter never coalesced into clusters, then no planets or stars would form. (How life would evolve in this type of universe I have no idea).
In fluidic space, the fluid seems to act like the vacuum in our space and somehow has no gravitational attraction either to itself or to anything else.