Why are world powers unable to stop Boko Haram?

Two years ago, the world watched in horror as 276 girls were abducted from their school in Chibok, Nigeria, by the group known as Boko Haram, a militant Islamist group that swears allegiance to the Islamic State of Iraq and Syria (ISIS).
Fifty-seven of the girls later escaped, but most have not -- and the situation has only gotten worse. The kidnappings prompted a global campaign, #BringBackOurGirls, but experts say
violence in the region has impeded the girls' rescue and the world's attention has shifted to other crises. I actually had the feeling that a change in power to a muslim leader might make a different.

Boko Haram, not ISIS, is world's deadliest extremist group, study finds to show how dire the situation has become, the U.N. children's agency, UNICEF, released a report on Tuesday showing that the number of children involved in  suicide bombing has risen tenfold in the last year in the Lake Chad region, which includes Nigeria, Cameroon, Chad and Niger.
The United States continues to assist the Nigerian government's efforts to locate and bring home all those who have been kidnapped by Boko Haram with intelligence and advisory support. Inspite of all aids and many more, my question goes thus; why are world powers unable to stop Boko haram?