They're cornered and when terrorists are cornered the fight to death. Check out battle of sirte
. All 2.5k of them were killed. Majority of AS leaders are in middle Jubba so capturing it is crucial. But removing AS from Somalia will take years tbh.
What is needed ASAP is taking their regional strongholds, places like Jilib in Lower Juba, Ceel Buur in Galgaduud, etc. These are towns with 60k+ people, If we can remove them from there the rest can easily be dealt with
The longer this takes however, the harder it will be to remove them from these places.