You used to even be able to get freshly made meat and vegetable dishes on the Guangzhou to Hong Kong (Hung Hom) intercity route.
High speed rail has for the most part either totally ditched the dining car or switched to pre-packaged boxed meals that aren't particularly interesting.
On my most recent long-haul slow train trip from Hong Kong to Beijing in 2016, a university professor from Beijing decided to sit across from and repeat government propaganda to me as if she was the first person to ever tell this foreigner who speaks fluent Chinese these things. "Did you know China has 56 ethnic minorities?" "Did you know China has 5000 years of history?"
I made a point to visit a dining car on an east coast Amtrak route several years ago after my amazing China dining car experiences hoping to get some of that traditional dining car experience and found to my disappointment that even then they were only serving pre-made meals.
I guess it's hard to justify pulling and staffing a full kitchen and stocking it with fresh ingredients.