It is not required by the nec in a residential attic.
Is conduit required in attic.
I m building a new home outside the city limits in liberty county in texas my electrician ran the main power feed wire from the meter through the exterior wall up into the attic and down into the breaker panel without any conduit.
Always check in with the local building code authority.
For this reason the nec has protection requirements for nm cables in an attic.
Conduit also protects your wires from exposed surfaces such as rough bricks in a basement.
Code requires that romex be installed in a conduit.
A loose cable like in the photo above gets caught in the spring mechanism of a pull down folding ladder at the attic opening and frayed.
Damaged cables can cause a short circuit or even worse arcing that will start a fire in the attic.
It will be easier to repair wires if there is a short in the line.