I don’t know why the trees grow in this particular way. I can only assume. Quite possibly, when these trees were “young”, they were damaged by some insect, people or an explosion in a way that their trunks broke to the point where they leant against the ground, but still holding together. Since the trunks were not completely broken apart, the trees had some limited nutrition and took some time to rise up from horizontal to vertical position. That could explain it.
Do you have a better explanation?