I haven’t traveled recently, but my understanding is that they are providing the boxed meals to sleeping car passengers because the dining car is unstaffed.
If that‘s the reason, and there is no staff, it will not be available to coach passengers either. The cafe is still open.
If you're in coach then you have access to the Lounge car cafe. If in sleeper, then it’s the “flexible” meal option. One other little known option is the ability to order Kosher meals, it requires 72 hours notice, but the meal are generally better.