Think of it as a sniper... shooting a person to kill them from 100m should be quite straight forward... the distance they can move between when you fire the gun and when the bullet strikes the target will be incredibly short so there are very few things the target could do to evade getting hit... especially if they don't know the bullet is coming.
Now think of that same sniper shooting a target 20km away... with a projectile flight time measured in minutes the obvious problem for the sniper is to anticipate where the target will be in however many seconds his projectile will be in flight towards the target... once you fire even a slight speed up or slow down of the target could create an enormous miss... if the target is walking along a path you might be able to anticipate his position x number of seconds later if he is walking at a steady pace... but what if he hears or sees something that attracts his attention and he stops or slows down or speeds up... for a flying object the problems are multiplied with an added dimension of altitude... it can speed up or slow down or turn left or turn right or climb or descend but it can also do any combination of any or all of those...
The solution is an air burst... predict an intercept point and then set the round to explode there sending a shower of fragments over an enormous area to compensate for any deviation in flight... it would be relatively cheap to implement... certainly cheaper than a shell that manouvers... though to be clear a manouvering round doesn't need to fly loop the loops or be some sort of modern day dog fighter... often just being able to turn a few degrees to deliver the HE fragmentation warhead closer to the target is good enough... even a ring of side mounted rocket thrusters to push the round one way or the other would be enough... or even a speed brake that flips out for a fraction of a second to steer the round one way or the other could be enough to get the HE round close enough to end a drone.
Drones are tiny but are also incredibly fragile and very easy to break... a shock wave could break the wings which could be enough to stop it being effective... you don't have to shred it with shrapnel fragments, or blow it into tiny pieces...
These systems are very interesting and have potential connected with an IADS where warning times are sufficient as it could be done cheaply but still efficiently too... together with a range of other systems including decoys and jammers and even your own drones with weapons mounted on them to hunt other drones... it would be very interesting...