I agree with you, but to use your Mumbai attack example, "everyone" (everyone I've read) basically believes that the Pakistan CIA-equivalent helped sponsor the

I agree with you, but to use your Mumbai attack example, "everyone" (everyone I've read) basically believes that the Pakistan CIA-equivalent helped sponsor the attacks. An organization taking responsibility for the attack would lead back to this organization, which would involve a lot of political drama. As long as Pakistan doesn't openly claim responsibility, there's no real loss in political capital to them- Indians hate them anyway, and any time an attack happens, India seems to rattle its sabers for a few months before backing down and they remember that Pakistan is also nuclear capable. Then business returns as usual.