[DonRotolo]

Sheet metal is a perfectly valid choice for construction, just as extrusion would be. However to be successful you need to use it properly.

Metal is metal, with some exceptions the same metal will have the same tensile strength in pounds per square inch - whether that's a 1" square or a 1/8" x 8" sheet. Which do you think would be harder to bend in the flat direction? In the wide direction?

Take a sheet of paper. Hold it at one end and swat your computer mouse with the other end. Then roll it into a 1" diameter tube - does the tube swat the mouse further?

Sheet metal uses the advantages of shape (geometry) to allow less material to be used for the same ultimate rigidity. However one must "do the math" for it to work as well as the relative brute force of 1/8" wall extrusion.