After fully onboarding your Scale Insights account with one of the regions, you may still find some marketplaces not showing up.
Scale Insights will not show the marketplace in the drop-down menu if you do not have any products in the marketplace.
In the screenshot example below, a seller only has products in the US and Canada marketplaces within the NA region.
The drop-down menu will only show the US and Canada marketplace and not the Mexico marketplace, as shown in the screenshot below.