Al-Shabaab is a mercenary, death squad group that does the bidding of whomever that paid them the most. It is very decentralized group, so different commanders do as they see fit without their leadership not aware of what the lower rank commanders are doing.
Foreign powers such as UAE, UK, and others have their hands deep in this group. When the TPLF was in power in Ethiopia, they also had their hands deep in Al-Shabaab.
Now, to blame it on any group or region in Somalia/Somaliland is disingenuous in my view. Most of the assassinations in Galkacayo, Bosaso, and Lasanod are carried out by UGUS. And that should tell you this monster is all over the country.