Seriously, it is something that's so annoying and distracting, even if really inconsequential. I don't know if they do these things over being nervous or if they are really laughing at their own garbage.
They are not the only folks in this world that are unable to control their nervousness and insert laughter at inappropriate moments. Thing is, leaders, world leaders, are not supposed to have this quality that much. This too screams weakness whenever it happens. It can also scream disrespect to certain listeners.
Kamala when she is speaking about remote learning for children:
Kamala with a few difficult questions:
Hillary on Somali piracy:
Hillary on her emails, the only one to find it funny, even when discussing national security and the FBI too:
Says Hillary's scariest laughs, but the important thing to note here are all of the serious issues she is laughing at: