Buildings and bridges have very large safety margins, to account for design errors, construction errors, damage, poor materials, etc.
Airplanes have much smaller safety margins, meaning a lot more calculation is done, and there's a high emphasis on double checking everything.
Spacecraft have tiny safety margins, which amps up the design rigor to 11.
Airplanes and srarcrafts are operated by a trained trusted crew. Software is operated continuously by lots of hostile people and machines.
When terrorists take the control of a plane, it's a catastrophe.