How Do European Students Complete PhDs in 3-4 Years While Maintaining Work-Life Balance?

I came across a PhD advertisement on EURAXESS, which mentioned a duration of 3-4 years. I know many students from Europe who have completed their PhDs within this timeframe. However, based on my experience as an MS student and research assistant at one of Korea's top research institutes, PhDs typically take 5-6 years to complete. In some cases, students remain for up to 8 years, but this is often because professors require them to work on additional projects, even after fulfilling their PhD requirements (e.g., publications) within 6 years.

I've observed a similar trend among PhD students in the United States. Moreover, in Korea and the US, students often work more than 10 hours a day as full-time research assistants. In contrast, I’ve heard that in Europe, students are not expected to work beyond 5 PM and are not required to put in extra hours. This raises an interesting question: how do they manage to complete a PhD in just 3-4 years?