If it were possible to use drones to kill Abubakar Shekau and other top leaders

[Recursion]

44. Nope.

Tons and tons of Pentagon studies on this; they didn't go to drones on a whim. It's a way to attack a target without the immense collateral damage associated with infantry and its artillery support.

A single high explosive 155mm shell from an M777 will flatten a three-story brownstone rowhouse and shatter every window for 200 meters. A single fire mission or barrage consists of 12 of these shells falling within 30 meters of each other. A platoon moving through an urban area can expect to call in a fire mission for about every 100 meters traveled. A battalion (the smallest unit realistically sent after a target) is 9 such platoons. So, 9 of those barrages for every 100 meters traversed, just to get the infantry into position to then attack. (And the infantry are bringing mortars along to do a smaller version of what the M777 does once they start the assault.)

Even without artillery support, infantry are absolutely devastating to inhabited areas. Consider the battle of Mogadishu (the primary reason infantry only move with artillery support nowadays): the best estimate is that 3000 civilians were killed in that fighting, all just to get Omar Elmi. That's actually a great example of when a drone would have saved thousands of lives: bomb the building he was meeting in, and that's 3000 Somalis who wouldn't have died that day.