Trolley service is more than adequate, Sheffield is two hours and Nottingham is ninety minutes. If we're comparing to SWR's 444s, the journey time to Weymouth is of course 3.5 hours.
Weymouth sits with the Highland Chieftain/Aberdonian and GWR Penzance services - they are unusually long services compared to the bulk of the TOC's operation, and while they could do with a different style of stock and on-board service it's not, because it would mean microfleets, sensible/economic to provide them.
EMR's journeys are all fairly short so you don't really need luxury and high levels of on-board service, you need decent comfort and maybe the opportunity to get a second coffee to the one you took on from a station shop as almost every coffee drinker will, and food can be taken on from Mark's or wherever.
Oh, I always get food and drink before I get on EMR.
Most people do. M&S Food and the likes are what's killed on-train buffets to be honest. And that's not solely a UK thing - DB have got rid of restaurant cars from ICs, NS got rid of on board catering years ago.
The most people want is a decent coffee on longer trips (though they'll almost certainly have carried one on to start with). A Nespresso machine on a trolley could do that.
And they wonder why 75% of people from Sheffield to London, drive.
I suspect there are two main reasons they do - overcrowding and high fares. I can't imagine most care whether there's a buffet or not, and First Class is irrelevant to the vast majority of people these days.