There is legal accountability though, and a much better understanding of who can be held to blame for what. Software suppliers are pretty much immune to consequences of carelessness.

However, I think the real problem is that software is far more complex than a bridge or a building. IT system have complex hardware (far more complex than any mechanical device) running even more complex software (counting all the layers from OS up). On top of that people (meaning users/buyers) have no idea how to evaluate safety/reliability/security and mostly seem to regard it as a nice to have to be traded off against other nice to haves, not an essential baseline.

Once its implement everyone assumes the computer must be right, and acts accordingly. The presumption that computers are right is even enshrined in UK law (the intent was to stop people getting out of things like speeding tickets by claiming speed cameras where faulty) but I think everyone has come across situations where the final word on a dispute was "the computer says so".