Even if motorcycle tires had kevlar beads, I can't imagine how you'd ever fold a steel belted radial, let alone something like a Mitas E07 bias ply tire. Plus, the forces exerted on a motorcycle tire under load are orders of magnitude greater than on a bicycle tire; maybe the wire reinforced bead helps the bead to resist deformation.
I don't know why motorcycle tires have steel reinforced beads, but some bicycle tires must share the same reason. My Panaracer Paselas on my Trek 520 have wire beads, as did some other ones I've used like the Continental Grand Prix.
"No matter where you go, there you are."