Wooden poles can be pre-drilled to allow for the installation of hardware fairly easily. Steel poles can be manufactured with built-in grooves for the same purpose; field drilling is also an option, as is welding parts.
For poles made of concrete, however, drilling is not an option. Hardware can only be cast onto the pole during the manufacturing process - not an easy process.
Because drilling, welding, and casting reinforced concrete poles are costly, time-consuming, and dangerous, external strap hardware has become a more popular method of attaching hardware to utility poles.