The strength of a round object comes from its surface. There is very little you can do inside to increase the strength very much. The easiest way to increase the strength is make it a larger diameter.
This example has stuck with me from a professor, break a pencil with your thumbs, the thumb side is getting compressed, the other side is getting pulled/stretched apart. Now think about that, right in the middle between the extreme compression and tension (+ and -) there is nothing going on, at some point between positive and negative is 0. that is the center of a pipe a pencil is dramatic because wood flexes, steel moves very little so the skin of the steel is doing all of the work the zero zone is very large. same class I learned that a single support midway under the outer rails will increase rigidity by a factor of 4!
Sorry that example comes into my head all the time. It was a class about bridges, those things are insanely engineered. Great class, amazing professor, I got a C-….