The 1968 "Carterfone" case permitted third-party equipment on to
AT&T's network. To that point, restrictions on hooking up unapproved
equipment was based in safety. With copper wires you literally could
kill someone or burn down an exchange with misconfigured gear. Still,
the bill passed on the grounds of fair commerce. With fibre, none of
that can be claimed. At worse a misconfigured fibre transceiver might
affect other communications and would be traceable quickly, as with
coax.