Because arming the Libyan rebels worked out so well.
New York Times:
When President Obama rebuffed four of his top national security officials who wanted to arm the rebels in Syria last fall, he put an end to a months of debate over how aggressively Washington should respond to the strife there that has now left nearly 70,000 dead.
But the decision also left the White House with no clear strategy to resolve a crisis that has bedeviled it since a popular uprising erupted against President Bashar al-Assad almost two years ago. Despite an American program of nonlethal assistance to the opponents of the Syrian government and $365 million in humanitarian aid, Mr. Obama appears to be running out of ways to speed Mr. Assad's exit.
With conditions continuing to deteriorate, officials could reopen the debate over providing weapons to select members of the resistance in an effort to break the impasse in Syria. The question is whether a wary Mr. Obama, surrounded by a new national security team, would come to a different conclusion.
"This is not a closed decision," a senior administration official said. "As the situation evolves, as our confidence increases, we might revisit it."
Mr. Obama's decision not to provide arms when the proposal was broached before the November election, officials said, was driven by his reluctance to get drawn into a proxy war and by his fear that the weapons would end up in unreliable hands, where they could be used against civilians or Israeli and American interests.
As the United States struggles to formulate a policy, however, Mr. Assad has given no sign that he is ready to yield power, and the Syrian resistance has been adamant that it will not negotiate a transition in which he has a role.
The opposition is still hopelessly divided (the Muslim Brotherhood is the only organized faction in the new opposition group), and jihadists from as far away as Pakistan continue to join with the Free Syrian Army to help defeat President Assad.
It is inevitable that any increase in the flow of arms, as well as their sophistication, will only help the jihadists in any post-Assad political environment. Obama may see that as a plus, however, given his support for the Muslim Brotherhood elsewhere. Nor is it likely that any increase in weapons we give to the rebels will make a decisive difference on the battlefield.
A bad idea whose time will hopefully never come.