> cant your government just change it?

Short answer: no. The federal government (Congress) can propose amendments, but ratification requires the approval of a 2/3 majority of the 50 states' legislatures (38/50).

And remember that in the US, the governments of each state are not just sub-divisions of the federal government, but totally distinct entities with their own constitutions, legislatures, elections, etc. The federal government has no direct control over the states, and thus can not force them to approve an amendment.

So, to change the US Constitution, 39 separate governments need to agree, and that's a pretty high bar.