Computer engineering is not substantially newer than aerospace engineering.

It's a matter of tradeoffs. If your webapp is unusable 2 days a year people will just do something else in the meantime. If your flight control software fails for two days a year planes might come crashing down. The former is tolerable even if unpleasant from a customer perspective, thus they don't pay for flight control levels of reliability.

And it's not like this is unique to software. It's the difference between a disposable plastic fork and surgical instruments.

To be fair, a big portion of high profile computer engineering failures involve attackers actively searching for vulnerabilities, which bridges and ships don't need to deal with as much.