It’s substantially more complicated than that smallpox samples keep turning up in the US [1][2]. Who knows how many samples were lost in the chaos of the fall of the Soviet Union. Smallpox was in every country on earth until relatively recently simply destroying samples isn’t enough. Hanging onto them in case we need a new vaccine is absolutely prudent.

https://www.wired.com/2014/07/cdc-found-pox/ https://www.historyofvaccines.org/content/blog/scab-story