I think that is spot on. A buffet car only works if you are one of a group of travellers who can go to the buffet to get the food and drink for your party while others look after your belongings and your seat.Problem with buffets is having to leave your seat. Maybe first class passengers are less concerned about taking their stuff with them (because they are surrounded by first class passengers.....)
Nowadays, I usually have a laptop with me at my seat and other stuff in a briefcase or other bag. When travelling alone, I don't want to have to pack all that up and carry it to a buffet car to wait for service, hoping we don't arrive at a station in the meantime and I lose my seat.
I think that is what has killed the old 'Dining Cars'. The idea of packing up all your stuff to relocate to another carriage for your dinner and expecting your previous seat still to be available afterwards is just unrealistic nowadays. We expect at-seat service on aircraft so I don't see why we shouldn't expect service of at least that standard on a train.