You can create systems that mimic intentionality, for example with animal AI that is attracted to water and food sources, prey on eachother, etc...
You can, but to fully model the effects of this intentionality and how it shapes the environment in return would be a LOT of computation, very little of which will ultimately be player visible. While the player can tell when something looks off, he won't really appreciate it when it looks better than just "okay". Also, as the lessons from the original systems of Ultima Online shows, players will just murder everything and move on, anyway. And animals are just the easy part. We CAN produce reasonably passable procedurally generated empty wilderness, aided by the fact that most players have never actually been there and therefore have relatively low and few expectations. Even those of us who do aren't going to spend a lot of time trying to track migrating deer in the game.
The place where procedural generation falls the flattest is dealing with human intentionality. Have you ever seen a procedurally generated building of any complexity that looks even halfway convincing as an actual building? The best possible outcome is that you just kinda ignore the fact that the building makes no actual sense and settle for just shooting all the generic red bandits in it. But what is this building actually for? How does any of it work? Why is it built apparently to serve no purpose except as a place to spawn random bandits? How do the bandits even LIVE here? These questions go totally unanswered as we shoot them dead and loot their corpses, but once you stroll through an entire city generated in this way, you start to realize this city makes no sense and is purely a set of randomly generated, nonsensical buildings, none of which serve any clear purpose except as places to kill bad guys.
In contrast, space is easy. For starters, players have very little expectation for how space is "supposed to be". The vast majority of anyone on Earth has never actually seen space, and have even lower expectations that game-space will be astrophysically realistic in any way, mostly because if it actually was, the game would likely be really, really fucking boring, since realistic space is really, really fucking empty. Space doesn't really have an ecology. Your random encounters will be prefabricated space structures placed at equally randomly spawned resource nodes and other points of interest, but because space is intrinsically uninteresting anyway, you won't notice that these are just randomly generated interests plopped in a vast void of nothingness, because a vast void of nothingness is what space IS.
for me 
