For the same reason that a crumpled up ball of wire is a bad antenna.
To induce an appreciable current, the magnetic field has to act on a wave-compatible portion of the conductor. The length and alignment of the wire has to resonate with the direction and length of the wave.
To induce an appreciable current, the magnetic field has to act on a wave-compatible portion of the conductor. The length and alignment of the wire has to resonate with the direction and length of the wave.