My new official “train guy” explains the no 11-pm train out of Union Station: (Sorry if I’m the only one vaguely interested in this thread):

There’s no 11:00 for several reasons. One is there isn’t enough
equipment because our rail system has been undercapitalized for decades.
Amtrak has position its equipment for the morning rush, where the
greatest demand is northward in the morning, so sending an extra train
out of Washington late at night cuts into that capacity.
There’s also the need to cover a reasonable amount of the operating
costs. There may be lots of people who want to take a train out of DC
at 11:00, but they wouldn’t be using it every day. As a result, daily
ridership would be low, and conservatives would scream that the train
should be cut. Those earlier trains do better for ridership because
they’re getting a good chunk of the Philly-New York market (the 9:00 is
out of 30th St at 11, and into Penn at 12:25 am) as well as travel out
of Washington.
Your 10:00 is scheduled to accommodate overnight travel to Boston (a
great way to go), and there’s a 3:00 because Amtrak has (and has had for
a long time) the contract to haul mail between Northeast Corridor
cities. That mail contract (which Amtrak wins in competitive bidding)
is quite profitable.