Thanks, everyone.
To rephrase my question:
Since Amtrak fills its sleeping cars pretty well even with schedules that don't minimize daytime hours spent on the train, and with inconsistent on-board services and inconsistent station quality, and since sleeping cars are presumably profitable, if Amtrak adjusted its schedules so that overnight trains left major population centers in the evening and arrived in major population centers in the early morning, wouldn't sleeping car ridership (from all types of customers) and profits materially increase?
It is true that European night trains disappeared in large part, but recently they've been expanding (see, e.g., Nightjet).