They've cashed in on very other human tragedy, many much worse than Boston.
Why shouldn't they cash in on this one too?
While totally life changing for those involved, on a global scale it was a fairly minor atrocity with three dead and 264 injured (in the bombing itself, not including the manhunt).
I'm afraid in this world money, and the pursuit of it, overrides all other considerations.
Sad and disgusting but true.