While Delta has free reign in whether it offers entertainment or charges for it, it is good business to add value to the customer experience. Airlines will never operate profitably unless they can figure out a way to make the customer experience more valuable than the ticket prices they charge.
It really depends on what you consider entertainment. Would I like a movie, or maybe some options of movies? Yes! Absolutely. Do I want to pay extra to visit family members for live entertainment. No! Absolutely not. If they plan to charge extra because they've hired a pop band to sing on flights, I'm out.
Don't we pay enough for the actually flight without having to pay extra for comforts that were once included? First we have to pay for refreshments (previously free). then its headphone and blankets. Then snacks, extra baggage costs, fuel tax and now we have to pay for the movie? I heard paying to use the restroom is next. Outrageous.
I don't think it is up to Delta Airlines to entertain people on the flights. I feel considering the amount of technology we have at our fingertips you can always bring a movie or a book. If they do offer entertainment it is just going to make the flight cost go up even more.