Obviously nobody knows. Whoever wrote those inscriptions apparently didn’t either. Even taking them at face value, however, the evidence that these “Sea People” systematically attacked all of civilization is extremely tenuous. There probably never was a power capable of kicking over all of the anthills and destroying civilization without leaving any other archeological evidence of their existence.
I've never heard that the Sea People were a cohesive force, attacking all of Bronze civilization in anything like a coordinated attack.
Waves of invaders can take many generations to wear down the native forces. They don't need to be allied in any formal sense, either. See for example: Saxons turning Britain Anglo-Saxon.
Well they were a people, who came from somewhere! Are you really saying that these battles didn't happen?