What situation applied in Iraq, requiring invasion, that does not apply in Zimbabwe?

Because Zimbabwe does not have a valid national security interest for the United States of America.

Iraq supports terrorism while Zimbabwe is only chaotic due to internal strife. Iraq is a threat to US while Zimbabwe is not. Thus, Iraq was invaded and Zimbabwe was spared.

Bush Jr & his buddies can't make such big piles of money in Zimbabwe.

Zimbabwe does not have oil.

the usual there is nothing to the advantage of America.

Zimbabwe is just in chaos and people are dying, no big deal.

There's no point spending taxpayer money to destroy stuff that'll fall down on its own, and killing people that'll die if we just let them be.

im gonna have to say oil haha