Thanks - You're true, but not quite what I was looking for.
(As far as reasons - if you are say, going hard thru a mud bog or something, and can't see that the far side is a vertical wall, as opposed to a slope out of the bog, then you may decrease speed fast enough to deploy the airbags, but for myself, I would not really want them to deploy. My seatbelt is good enough for 20km/h, for me.)