Because this is language of users, not quizzes. Many just play English quizzes. And also we lose money on Russian users since advertising is banned there from western companies, so it is not something we are willing to get involved in or put time into.
Most likely when those events gonna end, some of the sanctions would be removed and the advertising sites would be possible to show and click on, probably
Now waiting for the moment when Swedish will become a featured language... 😉