The one-shot adventure is designed to be played in a single evening, introducing players to a new game without a long term commitment.
The challenge for the Gamemaster is to introduce a new game and its system while also telling an interesting and engaging story.
From experience I can see that it is difficult to indulge players into setting, plot, world, characters in a single session. Even putting this aside, there is a problem of information – with no background experience of the plot and no vision of continuing, it is difficult to compress something good into this tiny timeframe of maybe 3-4 hours.
Keep it simple.
Keep it focused.
Keep it moving.