Let us use tennis as an example. Can Roger Federer conduct an interview in English? Sure. Can Ma Long conduct an interview in English? I have not seen or heard a single one. But that's a marketing issue. Has Rafael Nadel been asked to speak English in an interview on air? Yes. And Nadel's English is not as good as say Federer's. Has WTT or ITTF asked Ma Long any questions in English? No.
Let us not pick on Chinese players. Hina Hayata just won the biggest match of her career and some could argue one of the most exciting table tennis matches in the past 10 years. She is only 22. Yet her interviews were conducted in Japanese, translated by a translator. Enuff said. It is a lack of coordination and marketing effort from the top of the sport.
I do think you forgot one very important point.
Ma Long or Hina Hayata is speaking for their fans.
If Federer's fans was majority say French and can't speak English. I am sure he would have more French interviews, than a language his majority fans won't understand.
Since it is a global stage, and English is the international business language, but not the official Earth language, there is nothing wrong for the players to speak in a language that they few comfortable with.
Go look at the UN, or WHO or any world body. each will speak in the language they are comfortable with.
And saying they should speak one language over the other, is not necessary marketing. Since some understand, the rest won't. If you really want to make sense, irrespective on the language, I don't think that is a problem.
Now back to Table Tennis
China and Japan are the biggest and 2nd biggest table tennis market in the world.
If any, TT fans should be learning Chinese and Japanese.
Japanese players learn more Chinese than English, why? learning table tennis in Chinese is extremely important.
If you are bilingual, listen to Chinese table tennis commentary versus English. It's day and night apart.
Now coming back to the players and "schooling".
I'm not sure how many hours of schooling tennis and basketball athletes must have
But it is not uncommon that these elite TT players had little or no school.
Train 6 hours a day, school maybe 3.5 hours a day. it is almost a 2 to 1 ratio.
I'm not sure where they can find time to learn a language while being a junior.
Most I know, learnt it being a senior and playing the sport say in Europe for few years, and just become better over time. There is no time to learn anything as a TT junior in Asia.