If the ever devlope a form of a storage device capable of holding all of their thoughts, then you more than likely would not see this.
Just blame a majority of it on tech. limits.
It has nothing to do with tech limits. It's strictly a design decision. gamesas chose to have every NPC line done in voice over and then they chose not to do a few extra lines that would add flourish to the world. They chose. They were definitely not forced, not by time, not by tech constraints, not by the difficulty of implementation... They chose.
It was a cold and cynical evaluation of whether what they had would be enough to svcker in casuals or if they needed more. Nothing else. And because everything is done in voice art, it's going to be almost impossible for modders to do sod all about it without it sticking out like a sore thumb. And gamesas CHOSE TO MAKE THINGS THIS WAY.
There's no excusing it or dodging it, there's only accepting the cold, hard truth. gamesas made every choice regarding this game, nothing was forced by some external publisher, and they chose to not record more flourish lines, for the simple reason that all the simpleton reviewers and all the casuals wouldn't notice anyway, so really there wouldn't be a good return on investment in buying more lines from the voice artists.
You know what's really funny? it's all a matter of rank in a lookup table. In all the previous games since Morrowind, the NPC greeting (and all the other dialogue) is determined by which entry with matched prerequisites comes first in a table with entries. I'm guessing it's the same in Skyrim, which means it's hugely simple to add a few lines about the main events in the game. It is thus exclusively a matter of intent.
If modders could do voice art that even remotely resembled what is already in the game then the problem could easily be fixed for the PC segment, but modders usually can't do voice art worth a damn and so all the platforms are doomed to a stupidly static world, solely because gamesas couldn't be bothered with a bit of polish.
Best thing mods can do at this point is shuffle the existing dialogue around so guards only call you sneak-thief if you're wearing thief guild or nightingale armor and NPCs stop talking about you being a new member of the companions once you're not new anymore. It will be an improvement but won't fix the depth issue.