Has nothing to do with a marathon run, but all to do with the exposure it gave the bombers for their intended maximum impact in which they wanted to project with this choice. There was a message also, but sadly it was cut short by our idiocy in wanting to read terrorist their rights, and then provide them with lawyers who will defend the devil himself if they have to against America and it's interest in security here. I can't believe the way you worded this, as if to suggest that the marathon run was the motivated target by the bombers, because what they may have hated runners is what you are suggesting to us ? LOLTerrorism is generally motivated by a political or religious belief with the intent of forcing through the terrorist acts a political, religious, or social change that seems to be the case with Boston it did not with the other's mentioned in the OP.
Can you explain exactly how that seems to be the case with Boston??
The WTC, the Pentagon, a lesbian bar, an abortion clinic, a federal building, all have some political or symbolic significance. They're all charged with some kind of political mojo that the attacks on them opposed and wished to suppress via intimidation-- "political, religious or social change", as you correctly noted.
-- Now what exactly is the political, religious or social significance of a marathon run? What possible point can be made by bombing it? "Walk don't run"? Think about it.
Moreover, the bombers didn't identify themselves or take "credit". So how are we supposed to infer a political, religious or social message from ... nobody? Nobody by definition has no political, religious or social viewpoint at all.
Doesn't work.
It goes way beyond the target, and why they chose the target they had chosen, and just think if they would have made it into time square, would you still be in denial that these are terrorist ?