Because much of El Salvador's population lives abroad and supports their families back home with remittances, 4% of El Salvador's GDP goes to remittance companies like Western Union. If they can cut that by a factor of 4 or more by using Bitcoin instead, they can boost their effective GDP by 3-4% in a single year, which will help a lot with getting re-elected. (I have no idea what the corresponding numbers are for Panama; probably not so urgent.) Also, like their predecessors Wikileaks, Sci-Hub, and Library Genesis, they become immune to possible future US sanctions (official or secret) that try to cut them off from international trade.