That's lip service. The US has never been serious about the fight against Al Shabab.
Somalia is not Afghanistan, it's flat, with a few helicopters and a well-equipped battalion, including morally, could easily annihilate Al Shabab.
The US used to arm Al Shabab through Ethiopia.
The US wants Al Shabab to be around as long as possible, so it can continue its misleading money making business - "War on Terror." In addition, Al Shabab and Boko Haram are not a threat to the West.
By the same token, do you think Nigeria's army can't defeat the ragtag Boko Haram fuc'kers?
The truth is that the US unofficially refuses local governments to seriously fight these terrorist groups, neither does it want these governments to reach a peace deal with these groups.