In BR days, there were a variety of eastern termini. Harwich/ Ipswich/ Norwich/ Cambridge (and Stansted?)... there were services running via Nottingham and Loughborough (and some avoiding Sheffield, and the hourly service from East Anglia to Merseyside through the West Midlands)... and there were a variety of western termini (Liverpool, Blackpool, Cumbria)... the move to simpler timetables and the "simplicity" of privatisation simplified these... the later Central Trains changes fixed the Hope Valley service to run from Norwich (with all of the Cambridge/Stansted services running through to Birmingham).
The problem that the railway has is the balance between hundreds of different flows and trying to maintain a simple reliable timetable for regular passengers (e.g. the desire for a service at the same time each hour from Liverpool to Manchester or from Nottingham to Sheffield).
I know some people who moved from Norfolk to Sheffield when Norwich Union opened up here (people who do go back to see family etc in East Anglia from time to time)... I know people from East Anglian who came to University here (and I'm sure the same is true of Manchester/ Liverpool)... but are there enough people to justify a through service? For me, I'd rather have a service to Cambridge/Stansted, but we lost that when Central Trains was split up. I'm sure some would want an Ipswich train instead. And the same at the western end (I'd find a Blackpool or Cumbrian link useful, though I probably wouldn't use it more than once a year, so appreciate that my personal preference is an irrelevance!).
Ultimately, you're going to disappoint a lot of people whatever you do. You could have a complicated timetable where the Hope Valley service runs bi-hourly to Norwich and bi-hourly to Cambridge (with the Birmingham service similarly running bi-hourly to those places), but then that'd mean accepting a 30/90/30/90 split from Peterborough to Norwich/ Cambridge which would mean prioritising a small number of long distance passengers over the larger number of people doing short distance journeys.
Plenty of other cross-country (=/= XC) links have been lost over the years without as much fuss - I guess that some of the complaints about this cut are because the Norwich - Liverpool service is one of the few such routes left - a corridor leftover from BR that doesn't neatly fit into TOC boundaries. But if it means getting five coach TPE trains through Sheffield then the loss of a Norwich link is a price worth paying for me (and inconveniencing the people I know who travel back to Norfolk once a year is a price worth paying to benefit the people I know who commute daily from Chesterfield/ Manchester/ Stockport to work where I do, or the people I know who commute from Sheffield to Manchester/ Nottingham).