A possible motive would be to spin it as the fault of a right wing loons video (which they can't control) instead of a left wing security failure (which they can control, at least to some extent).
Local witnesses in Benghazi said that the attackers stated it was because of the video, and there was
also a severe security failure. Why do you think it had to be one
or the other?
Seriously, on 9/11 of all days the closest security backup forces are in northern Italy and all they had were 9mm pistols? Who thought that that was a good idea?
No one, since that's not true.
The closest fighters were in northern Italy. The closest backup security force was Charlie Company, 1st Battalion, 10th Special Forces Group, on a training mission in Croatia. This group is specifically
for responding to important threats within their geographic area, and Obama ordered them to deploy at 2:39 AM, Benghazi time (20 minutes later, he also ordered the deployment of Delta Force from the US). Because ordering a deployment like that doesn't exactly work the way that it does in movies, it took time to assemble the groups, vehicles, transport aircraft, and mission plans. The two groups arrived at staging bases in Italy late the evening of the 12th of September, Benghazi time. In the meantime, a Marine team in Spain had also been ordered to deploy, and arrived directly in Tripoli at about the same time.
The men with 9mm pistols were a small four-man group assigned to survey security around the Middle East, and were not part of any "backup" group or either of the two above groups, and were
already in Tripoli when the attacks happened.