Why is she leaving?
-I recall there being some hooplah in conservative circles a year or so ago about "Psaki leaving because she can't handle spinning all of Brandon's lies" or something, which is obviously bullshit.
I think she had announced that she only planned to stay in the position for 1-2 years because, frankly, it's a brutal position when you actually do your job.
Stay on top on the pulse of public opinion, make sure you understand the President/admin's stances well enough to properly represent them, then go out every single day and do the crossfire thing with the press (well in Psaki's case) then watch your hones responses get picked apart and misrepresented on news channel x/y/z, then have to deal with the public's perception of the entire admin on a daily basis in your private life.
I wouldn't want to do it, most of the prior admin's press secretaries didn't want to do it, and after a while Psaki doesn't want to do it either.
Her run has been impressive to say the least.