If the conversations are “professional” in that they hold the other nations and leaders in proper respect then why should they be classified?
Granted things which talk of exact/non-hypothetical weapons and defenses do have some justification for being classified... but I think it would ALSO so us well to remember that Tom Clancy’s Hunt for Red October got him pulled in front of Congress [I believe] and questioned for the breaches of security regarding classified capabilities of submarines (which he reconstructed from non-classified sources if I remember).
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.