Most light aircraft don't have a convenient mounting location on the instrument panel for an airbag. You can't really mount it in the yoke, since the yoke would move during deployment (and I'd hate to see what would happen during an accidental deployment close to the ground...) Therefore, the seat belt is really the best place to mount them. All Cessna 172SPs I've flown feature the airbag in the seat belt - it's not a bad design either, it's comfortable and really not that noticable when in place.
Cirrus types are some of the best equipped GA
aircraft when it comes to survivability. In addition to the CAPS airframe parachute systems, most Cirrus come equipped with airbags of various types, and all come equipped with "CEATs" (Cirrus Energy Absorbing Technology) seats. The CEATs technology essentially mounts the seats on collapsible high density honeycomb blocks. The blocks are designed to crush vertically and lessen the vertical deceleration forces transmitted to the occupants in a crash. Since humans are far more sensitive to vertical acceleration than transverse, I personally feel more comfortable with a well designed (controlled deformable) seat in conjunction with a four or five point seat belt than I would feel with simply an air bag.
I reject your reality and substitute my own...