Keystone Service is funded in great part by the Pennsylvania Department of Transportation. As is often the case, funding, funding, money, funding, money...............Pennsylvania is in a budget crisis at the moment with the new Democrat Governor locking horns with the Republican controlled legislature, is operating without a formal budget on stop-gap legislation bills and who knows what the future could be?
Yes, a cafe car wuld be nice but can't see where it would be econonomically viable, considering the entire route is only 4 hours and as you wrote, doesn't have a Business Class level of service.
Keystone is basic "commuter service", not much more than any local transit service with UNreserved service in PA. Albeit an important link for Harrisburg, the furthest Western station to link with the greater North East Corridor, which is WHY PA funds this service.
Money, money, money..............when that train sells out at 75+% of the time, then you might start to see expansion of services offered. I've ridden this train a number of times now and the train is 75% EMPTY from HAR to PHL with the majority of passengers boarding at LAN (Lancaster)............Actually, I'm genuinely surprised PA continues to fund this obvious "money-looser", but as a PA Taxpayer, I'm glad PA does continue to fund this train and hope it continues and ridership increases. Time will tell...............