"The precise impetus for the bounty remains unclear. It’s certainly the case that the US has been more concerned about the potential threats LeT poses since Mumbai.
And it is possible additional evidence came to light that spurred this action. Specifically, some reports suggest that evidence collected from Osama bin Laden’s Abbottabad compound during the 2011 raid in which he was killed suggested he had been in touch with Saeed regularly. LeT’s precise relationship with Al Qaeda remains the subject of significant debate, but if true then this might have spurred the US government to take this action.
In some respects, the more important question is what the US hopes to accomplish. Given that Saeed is not difficult to locate, it is possible this was intended to signal the seriousness of US concerns to Pakistan and pressure it to rein in Saeed (and through him LeT) via a practice of naming and shaming. This decision also might have been taken in an attempt to put pressure on the group directly."