Belt Up!

OK, riddle me this: how come spaceships in sci-fi series, no matter how sophisticated, never have seatbelts to keep the cast from being flung all over the place whenever the ship experiences the slightest jolt? For crying out loud, we’re a few laws away from shooting people for not buckling their seat belts when they’re parked, yet Captain Picard gets flung out of his chair every time someone farts in engineering.