They are not 300,000 electric cables. They're large diameter coax cables. They pass radio signals from the radio cabinets at ground level to the antennas at the top of the tower. They also pass low voltage (12V or 24V, depending on design) up the copper outer jacket to power amplifiers for higher dB radio signal, as the higher the dB, the shorter the propagation.
I build cell phone infrastructure from 2000 to 2010 for AT&T Wireless Services, Cingular & then at&t, post 2004 merger.