And we all know that spider web is stronger than carbon on a weight per weight basis, but I haven't seen a frame made of it yet. Steel has a high shear strength, you will not see carbon fiber used in nuts or bolts, which gives lie to the idea that carbon is stronger. There are only a couple ways in which carbon is stronger than steel, and many ways in which steel is stronger than carbon.

One problem with carbon is that it is bonded with polymer, which dries and breaks down over time, and with exposure to uv light. Oscillation from riding and breakdown of perishable substances will eventually result in deterioration. The same thing happens to steel from oxygen and oscillation, but on a much slower scale.

I used to practice achery, and loved when carbon arrows were introduced. But then my shooting improved to the point that I was constantly splitting arrows, and carbon arrows are expensive. I went back to aluminum arrows, as I could straighten them out after hitting them with another arrow.

If you buy a light steel frame, and do the basics to keep it clean, your great grandchildren will be able to enjoy it when they are old enough to ride. I doibt the same could be said about carbon.