Anti-aircraft technologies rely upon radar, things which fly at low altitude are tough to track and hence cruise missiles skim above ground or sea to avoid detection. The small size of drones make it even harder to detect, cheap 3D printing technologies has also made easier to print composite materials with radar absorption/deflection properties for drones.
The shortcomings of current counter-drone tech was briefly mentioned by me in the need gap. Jamming radio signals to drone is useless when it has auto pilot, even time based or primitive mechanical auto-pilot would defeat this attack. GPS spoofing attack could deter drones using GPS based navigation, but it cannot be used in the areas which are sensitive to GPS usage such as cities, airports etc.
Physical attacks on drones itself is effective, provided the area is uninhabited to prevent injuries from falling debris. But if the adversary is a drone swarm consisting dozens of drones, physical attacks might not be even possible. Besides, the cost of deploying these measures are multi-fold compared to cost of deploying a home-brewed drone for attacking vital installations.
Hence I feel there is a large need gap for efficient area denial counter-drone technologies.