Basically, 3D allows you to see more sides to the issue, or immerses you in the situation.
But you can achieve the former simply by commanding the image to rotate, regardless of whether it exists in a volume of space, on a flat display panel, on a curved helmet visor, etc. And the latter isn't all that
useful for us poor humans who only have two eyes, both pointing forward - it does much more for situational awareness if you take the observer out
of immersion, and instead concentrate all the information conveniently in front of him.
So "freestanding", "holographic" views aren't really all that advantageous. Sure, they may be pretty, but they may well be far less informative than non-freestanding three-dimensional views. Say, you have a conference at Observation Lounge and want your officers to view the schematic of the enemy fortress from all sides to find optimal ways in. If you have one beautifully freestanding holo-fortress there, rotating above the conference table, it's user-hostile: if LaForge is looking at the front gate, Worf must settle for looking at the rear ramparts, and if they rotate it, one wins but the other loses. Much better to have separate images for each officer - and those don't benefit at all from being freestanding.