Senior engineers have less opportunity to write time consumingly careful code because they get paid so much. Much easier to throw new great hardware at it.

Senior engineers have less time to write code period.

And this is what saves the day.

Code is a liability.

The corporate structures that reward people who prove especially good at building the product with more meetings and less time building the product are perhaps not optimal in their deployment of resources.

Maximising the fraction of the product built by people who don't know what they're doing would however explain the emergent properties of modern software.

Senior engineers can write time-consuming, careful code efficiently. This is why they are seniors.