It's still in there.

You can find the US state standards used to set baseline requirements ("learning standards") for school district curriculums online, for most (all?) states.

Let's take an infamously-bad state for education ("Thank God For Mississippi") and famously good one (Massachussetts).

Cmd/ctrl-F "hamm" on this one to find it for Mississippi:

https://www.mdek12.org/sites/default/files/Page_Docs/final_2...

(Theirs is a little weird [probably because their government's, you know, bad] and this comes from a non-profit organization, but it seems to in-fact be the official curriculum standards for their actual BOE, as well)

Here's Massachusetts:

https://www.doe.mass.edu/frameworks/hss/2018-12.pdf

Same deal, you'll find it with a search ("Hamm" also finds one occurrence of Muhammad, in this case, though, but it does get a few hits on Hammurabi)

A person may have missed it due to: 1) going to schools outside the US that maybe don't emphasize Hammurabi, or 2) moving between US school systems that don't teach Hammurabi in the same year(s), such that they leave one before it's taught and arrive at the other after it's been taught.

Another very likely explanation is that it WAS taught, but was simply forgotten. Which is completely forgivable.

It's not like 6th grade had an intensive 3 month unit on Hammurabi.