Twin Towers was a mistake.
It was an accident that we inadvertently caused by a parallel incident in a
parallel universe that had a simultaneous synchronous occurrence on Earth.
The collapse or ending of the rule of the Twin Brothers in the parallel
universe and our mistake in thinking of humans and Earth at the same time -
caused this collapse of the Twin Towers.

Initially it was purely the collapse of Twin Towers for no reason at all.

But humans like to have reasons and like to have things explained - so the
two aircraft were produced as the reason or explanation.

Humans like to explain things like the beauty of the sea and the wonder of
clouds and falling rain in much the same way. They cannot simply accept the
nature of the Divine - they like to pick and poke and explain by way of
science and long ago acts of Divine nature such as the collapse of Twin
Towers for no reason had to be changed to suit the rather boring mundane and
none imaginative human - who likes to have nice logical explanations for
miracles and beauty and things Divine and mysterious in nature.

The two suicide bombers were two Borg who were transported and removed off
the two aircraft immediately prior to contact.