Linear antennas are simple, cheap, light, durable and work well enough. They do suffer from polarization and multi-path interference. These issues are mitigated with circular polarized antennas. On the sending side, circular polarized antennas send usable signals regardless of orientation. On the receiving side, they capture polarized signals and– when using matching circular polarized antennas– drop multi-path interference leading to a cleaner picture. In the above video from Neil DeLillo, you can see this difference in actual real-world use. Here’s the full article that explains the difference in detail. Basically, it’s weight/durability vs picture quality.