I suppose that if you really want to get into it you have to take time into account, meaning in-game/universe time. MW/Obliv is kinda idiotic in that regard since you can master skills in little to no time (a month? two?), which then ties to other aspects of the game world.
An example, I guess, of kind of an extreme -maybe- would be ADOM. You can start mastering skills by applying them, AFAIK, like the weapon ones, but time keeps running. You start losing resources like your hunger levels, and eventually the corruption by chaos in the world starts to eat it, again as far as I know. There you dont have all the time in the world to master every skill.
That's where the beth sand box model falls. The world is static, nothing ever happens if you dont start it, hence time or age have no effect. Obviously for the purposes of a game you can expect to master a few skills in a short, unrealistic time, but it sure is a long shot to be able to master EVERYTHING the game offers with one character.
It ties to the hand holding much loved by the codexians/hivemind, ties to the no real consequences for the things you choose (if any). No pain no gain, without sacrifice things feel empty, as cliched as it sounds.
Example: being able to be head of many guilds at once. Both stupid and unrealistic (in in-universe terms; were it to happen it'd be a major political shitstorm, which as far as I know does not happen in MW/Obliv).
And this is just in gameplay/game mechanics term. Narratively, I dont think you can justify mastering all the goddamn skills either.
It's just as simple as playing Doom with IDDQD (god mode) all the time. Why play the fucken game then?