“Swedish exports of ball bearings” are commonly brought up in historical discussions of World War II. Why were other countries so reliant on Swedish ball bearings and unable to produce enough themselves? : AskHistorians

I recently watched the Kings and Generals video Why Didn’t the Nazis Invade Sweden? DOCUMENTARY where this factoid was brought up again.

While I can understand how Swedish iron ore was in high demand (because Sweden has been a major iron producer for centuries and Swedish iron ore is high grade), what was stopping other countries, such as the UK, USA and USSR, from making their own ball bearings instead of having to import them from Sweden?