Sweden has been a strong supporter of the Kurdish cause for a number of reasons.
Firstly, Sweden, in their words, has a long history of supporting human rights and democracy. The Kurdish people have been fighting against Turkish state for decades, and Sweden has been a strong supporter of their struggle. For this reason, Sweden has provided financial and political support to the Kurdistan Workers' Party (PKK), which is considered a terrorist organization by Turkey.
Secondly, Sweden has a large Kurdish population. There are an estimated 100,000 Kurds living in Sweden, and they have been a strong voice in support of the Kurdish cause.
Thirdly, Sweden, in their words, has a strong interest in peace and stability in the Middle East. The Kurdish people are an important part of the Middle East, and their struggle for self-determination has implications for the entire region.
But, there is more to the story...
Supporting Kurdish separatism is not the only reason behind Swedish-Turkish spat. Turkey's opposition to Sweden's membership in NATO is based on several other factors, e.g., its arms embargo on Turkey, and its failure to extradite Turkish citizens who are wanted by the Turkish government.
Sweden has imposed an arms embargo on Turkey since 1984, in response to Turkey's said human rights abuses against the Kurdish population.
Turkey has accused Sweden of failing to extradite Turkish citizens who are wanted by the Turkish government for alleged terrorism-related crimes.
Finally, Turkey's strained relations with Sweden are part of a broader pattern of tension between Turkey and the European Union (EU). Turkey has long sought membership in the EU, but its progress toward that goal has been slow and contentious. Many EU member states expressed concerns about Turkey's human rights record, democratic institutions, and foreign policy.