The original FCC mandate in the Communications Act of 1934 was:
For the purpose of regulating interstate and foreign commerce in communication by wire and radio so as to make available, so far as possible to all the people of the United States a rapid, efficient, Nation-wide, and world-wide wire and radio communication service with adequate facilities at reasonable charges, for the purpose of the national defense, for the purpose of promoting safety of life and property through the use of wire and radio communication, and for the purpose of securing a more effective execution of this policy by centralizing authority heretofore granted by law to several agencies and by granting additional authority with respect to interstate and foreign commerce in wire and radio communication, there is hereby created a commission to be known as the Federal Communications Commission, which shall be constituted as hereinafter provided, and which shall execute and enforce the provisions of this Act.
It has always been for communications by wire and radio. I'd argue fiber optics are just a fancier kind of wire from the understandings of what the intentions were back then.