science fiction its totally easy with projection screens and the like
Not at all. Ads for contemporary commodities in a science fiction setting may undermine the artistic integrity of the setting. Same goes for fantasy.
In fact, the same goes for any game with a non-realistic artistic/thematic style. I suspect that advertisers will want to plug their generic pre-made adverts into games rather than take the time to create adverts that are tailored to the visual/thematic styles of the games that they are included in.
Adverts potentially stifle creativity and originality and disrupt gameflow and immersion.