Why is coaxial cable the most common feed line for amateur radio antenna systems?
Why Coax wins on convenience, not performance. Because the outer shield confines the RF field inside the cable, coax can be run alongside metal, through walls, taped to a tower leg, buried, or coiled up without upsetting its impedance or radiating, and standard connectors like PL-259 and Type N make hookup quick. Balanced open-wire line needs spacing from conductors, careful routing and usually a balun, so most hams accept coax's higher loss for the easy installation.
Watch out The low-loss claim is the trap: at the same impedance and size, open-wire or ladder line normally has less loss than coax (and is usually cheaper too), while large hardline or open-wire handles more power.
Coax is chosen for convenience, not for being lowest loss, highest power or cheapest.