At a height of 10 feet, the horizon is 4 miles away. Something coming at mach 5 ( 3,805 mph ) will cover that distance in a little over one second.
That gives the laser system one second to acquire the missile, point the laser at it, GET WEAPONS RELEASE PERMISSION from the captain, shoot at it, and do enough damage to take it out.
Even if the captain has already given permission for the system to automatically fire upon anything moving faster than Mach 1, that's still not much time.
Not many captains will be willing to risk inadvertently shooting at a ghost signal and hitting a friendly or neutral.
“At a height of 10 feet, the horizon is 4 miles away. Something coming at mach 5 ( 3,805 mph ) will cover that distance in a little over one second.”
3805 / 3600 = 1 mile/sec
“At a height of 10 feet, the horizon is 4 miles away.”
Radar is much higher resulting in a detection distance of 15 to 20 miles.
“At a height of 10 feet, the horizon is 4 miles away. Something coming at mach 5 ( 3,805 mph ) will cover that distance in a little over one second.”
Please source the capability to fly 3805 mph at 10 feet.