The safety requirement for the Commercial Crew program was a probability of fatality of no more than 1 in 270. Which would be absolutely atrocious for any other

The safety requirement for the Commercial Crew program was a probability of fatality of no more than 1 in 270. Which would be absolutely atrocious for any other mode of transport. And Boeing couldn't even achieve that much. I think the real issue is that it's just still very, very hard. Margins are extremely thin. Airliners are extremely safe despite existing in a realm that's inherently dangerous because they spend margin on safety. You could make an airliner that's way lighter than what's currently flying if you didn't care about making it robust against, say, hitting a weather balloon. But the ability is there to protect against adverse events like that. Spacecraft have almost no margin. The distance between normal operation and having a bad day is really small because getting people into orbit at all is still just about at the limits of available technology.