“We”? You mean that’s standard policy at consulates and embassies all over world? US military doesn’t give protection? The US always hires local thugs and fools?
The State Dept pukes don't like using Marines. Healthy, horny young men in a country where alcohol and fooling around with the local women are forbidden pastimes, will find ways to get into trouble and embarrass the suits.
Then again, when the jihadis are coming over the walls, the "local security" disappears down an alley, and all you have for security are any armed Americans.
For the suits in DC, having armed Marines presents an additional problem: they are more likely to open fire rather than allow themselves to be meekly slaughtered.