They will fix it soon.
The OECD is trying to change the test to be about more than academics, in part to encourage countries to view education beyond traditional subjects. In the latest test, it assessed global competency, asking students to express how they relate to others and what they think of their lives and their future; in the next test, in 2021, it will assess creative thinking.
https://qz.com/1759506/pisa-2018-results-the-best-and-worst-students-in-the-world/