The Ventilation Shaft

Why is it that in every science fiction movie, sooner or later the good guys always escape through the ventilation shaft?

From Star Wars to Lilo & Stitch, whenever the bad guys are chasing somebody they go in theere.  Need to get out of jail, go through the ventilation shaft, somebody about to shoot you, jump in the ventilation shaft.

Why can't these "advanced" civilizations with their "lasers" either monitor inside the ventilation shaft or make them transparent for gods sake?

If I was filming a science fiction movie and the good guy ran away the scene would go like this

Henchmen #1:  Commander Zoltar (always need either a Z in the bad guy name or a 'ar' ending, if possible both) the prisoners have run away.

Commander Zoltar:  Check the ventilation shaft immediately!