Because those leaders may be taking great risks with their own constituents by cooperating with the US, helping us to secure our own interests.
For example, the Yememni leader, at great personal exposure to himself and his government, allowed us to launch attacks inside his country. That is going to be a HUGE problem for him with respect to his own extremists elements in his country. That leak, while not at all discussing America's "secrets", increases our risk at home and abroad.
Hm, good point; I hadn’t considered it.