My theory which I've posted before, is that, as the operator of the Penn Line for MARC, Amtrak has an interest in discouraging talk of such extension of service or, for that matter, weekend service on the line. But that's not the major factor(s), which are mainly cost and projected ridership. The thing is for commuting all the way from Wilmington to DC, a lot of people would rather have the amenities of an Amtrak train. I see some semi-regulars on the cross-honored Amtraks who obviously commute to/from Philadelphia or Wilmington to DC. Whatever they are paying, they aren't there every day, just some days, and I doubt they'd want to make the trip in a MARC bilevel, even though they are darn comfortable as commuter cars go.
Of course, I wish MARC was like NJ Transit and I could take a cheap train from Aberdeen to Philadelphia on the weekends, that sure would be nice. (does NJ transit have any lines at all that are weekday only!?) I just don't see it happening for a long time. As it is at least monthlies can take a weekend Amtrak to DC, which is not a bad deal and kind of makes me hope MARC and Amtrak continue to "get along". Maybe since Amtrak already said no to weekend service once before, MARC doesn't want to poke the hornet's nest, so to speak.
What I think IS really stupid and could change right now, is why doesn't one of the afternoon Perryville bound trains do a return service? A conductor told me people ask them about it frequently, so there's some kind of demand. Even if it's only a couple people, what's the harm? The train is going back to Balto. Penn to do another run. It's not like they can breeze through that station at 125 to get back to DC more quickly. (not the last of course, that arrives at perryville at 10:30pm on a good night!) Well, we know MARC would have to pay Amtrak more for the revenue service, but it's not very hard work for the employees. If you must, confine people for the deadhead trip to the cab car so it only takes one employee to keep an eye on them or whatever.