Free space optics links are quite finicky even between stationary ground stations. Additionally, LoS communications are limited by the horizon. The mast antenna

Free space optics links are quite finicky even between stationary ground stations. Additionally, LoS communications are limited by the horizon. The mast antennas on most warships are something like 40 meters tall, meaning it's only 20 km to the horizon. Ships operating as one group routinely spread further than that. NoS communications on ships just use satellite links, which are also difficult to detect or jam if you're not along the axis. There are directional LoS microwave links used in some contexts, such as China's stations scattered around the South China Sea. The pointing/stabilization issues are much less severe with these.