Insufficient liability, one would guess. Cars, airplanes, industrial plant, all these have software in them but the liability is wholly different, should an accident happen due to a software bug.
Liability should first rest with the entities deploying the software, since those are the only ones with a picture of what can go wrong in the context where it's being deployed. Those entities should then be demanding warranty/indemnity as appropriate from their suppliers (or possibly third parties, for F/OSS).
Compare this attitude with the extremely conservative approach in rocketry. The technology is positively from the stone age, but everyone agrees that it is well understood. You can't take any other approach when space missions are multi-decade projects and the price tag has nine figures.