Space legs isn't "difficult", in any real sense. Nor is all the stuff that goes around it. "Difficulty" is NOT the reason we can't get up from the pilot's chair and walk around yet.
We have the pilot model, customizable with deformers and alternate skins to give us holo-me. The evidence for this next part is a little sketchy but if that model isn't already fully rigged and capable of being animated I'll eat my remlok.
Making the scenery to walk around IN, aboard your ship and within the station isn't "hard" - and some of it has clearly already been done given the "interesting" viewpoints some folks have achieved by piloting their camera into odd places. It is, however, time-consuming. Seriously time-consuming. Stations, settlements, outposts and megaships are easy. There's a reason that when Star Trek needed a low-budget episode it happened in caves or entirely aboard the ships. Creating a "set" with 3d modeling is no different, if it's all interior/technological it's a lot easier and takes a lot less time than an organic environment.
Similarly wrapping the code around moving through that set isn't "hard" either, it just takes a lot of man-hours.
Right now, with "what it's possible to do in the game", space-legs isn't worth Frontier's time.
When we have worlds we can land on with breathable atmospheres and a biosphere to explore, when there are not just sealed settlements but cities on worlds that we can land on, then space-legs will potentially be a thing. Not before.