It does reek of corruption, but it seems being ambassador to a close ally is basically getting several years of taxpayer-paid vacation in Europe. They're positions that have to be filled, and a career diplomat ending up in Sweden might even get bored because of the lack of anything to do.

For example ambassadors to Georgia (a country that has tensions with Russia) seem to have "better" credentials: https://en.wikipedia.org/wiki/List_of_ambassadors_of_the_Uni...