[benjaminl]

The key thing to remember about rockets is that they are incredibly fragile. The rocket is about 15 stories tall and is designed for force to only be applied at the end either via the rocket engines or the landing gear.

Any type of lateral forces will irreversibly damage the rocket. As an illustration, extreme care is taken when the rocket needs to be transported on its side. Some rockets, not the Falcon 9, can't even be transported on their side without being pressurized.

So pretty much anything other than a perfect soft touch landing would leave the rocket unable to fly again. Anything touching the 3/16" thick skin of the Falcon 9, would cause the very least extensive refurbishment at the least, but more likely irreversibly damage the frame of the 15 stories tall 1st stage. So this rules out every alternative that has been suggested in this thread.

[Dylan16807]

While that's true, the metal tube is not the part that's expensive to build.

[sbierwagen]

You'd be surprised: https://en.wikipedia.org/wiki/Isogrid

[tavert]

SpaceX mostly uses friction stir welding to avoid the costs of isogrid