As of 2018, Why did the governments of Germany and Sweden decide to receive refugees from Syria?
Were there any strategic/tactical political/economic factors involved?
Starting in March 2011 there was a major civil war in Syria, many people were displaced by the fighting and tried to escape, to Turkey and to Europe. There were a great number of refugees, many living in miserable conditions.
Many countries across Europe offered to accept refugees, as part of their humanitarian duty. Refugees often go on to make a positive contribution to the country that offers them asylum (I think of European Jews that escaped to America in the second world war, or the Ugandan Indians the settled in the UK having been expelled by Idi Amin), but it is not at all clear that this was the prime motivation. Instead it seems to have been a political response to demand for a unified action on refugees, and a desire to be seen as a leader among the European nations.
For Germany in particular, the people remember with gratitude the refuge offered by many nations that were victims of the Nazis.
For Germany, article 16a of the constitution in general guarantees asylum to those victim of political persecution. Furthermore, Germany (and Sweden) is a party of the Geneva refugee conventions of 1951 and 1967. Finally, they are both EU members and thus subject to directive 2011/95/EU which handles subsidiary protection for people who do not qualify for asylum according to the constitution or as a refugee according to the Geneva conventions.
All of these regulations and treaties predate the events of summer 2015 by years if not decades. Both countries have been receiving asylum seekers, Geneva convention refugees and those eligible for subsidiary protection (even if that was not a term yet) for decades. Why should they stop?