Disclaimer: no real experience. I would also say that I suspect it is much easier to ensure and test quality of steel. Ensuring every square inch of compound m

Disclaimer: no real experience. I would also say that I suspect it is much easier to ensure and test quality of steel. Ensuring every square inch of compound material like carbon fiber meets all requirements is much more difficult. Steel can be made pretty uniform in large quantities, shapes and sizes. On the other hand carbon fiber can easily have local faults ingredient imbalances, etc. that will be difficult to detect but might significantly affect strength of the material. In case of a huge rocket it does not matter how small part of it fails, even a single substandard square inch of it might cause entire rocket to fail catastrophically. I also understand that steel fails in relatively predictable ways compared to compound material. Carbon fiber has different properties in different directions which depend on how it was layered and that is probably going to cause any calculations to have potentially very large margin of error. As building the rocket is very much about calculating how much can be shaved off, unpredictability in material performance might be a huge issue.