Frankly, the only thing stopping Amtrak from doing this is unwillingness to pay for good food.
I mean, yes--if you pay enough, someone will come up with a higher quality good.
However, realistically, Amtrak does not have nearly the wide array of vendors to choose from as DB does. There's more Long Distance diners leaving Munich between Noon and 9 PM as there are on the entire US National Network in any given day (even in Daily Service).
Of course, there are no trains that leave Munich that cover nearly the same range without an in-station resupply as any of the LD trains in the Amtrak Network. They are all run out of Chicago and with few exceptions supplied out of Chicago. That is another challenge. How many national vendors will service two trains a day out of Denver? Two trains a day out of Kansas City? Etc.
That, and food quality in general is better in Western Europe and Germany. The portions are much smaller, generally, but it's still almost all exclusively reheated food.
To improve the dining options, Amtrak really has to partner with vendors that can reliably provide catering to urban train stations throughout the country as well as centered in Chicago. This is entirely doable, but Amtrak lacks the imagination and budget to make it happen.
The underlying point is that people are going to take LD trains regardless of the food options. The demand for LD travel is a "captive market". What Amtrak has always struggled with is growing that market with more innovative soft products.
I have never understood why they have not encouraged conferences "on a train", or thought about adding conference rooms or other things that would encourage larger group bookings. There's probably a ton of other great ideas out there that Amtrak hasn't contemplated that go well beyond just enhancing the dining options.
The other underlying point is that it doesn't matter what's on the menu, until the OBS is consistent in quality and procedure--no amount of logistical magic will make up for what is often unacceptable service.