The full form of the discussion is here:
So it looks like TPE have decided to switch the Liverpool to Scarborough service with the Manchester to Hull service and change it to Liverpool to Hull and Manchester to Scarborough...
www.railforums.co.uk
The short summary is that it balances out the rolling stock in the best way not to have services from Scarborough running through to Liverpool any more, so that locomotive hauled trains and 802s don't work to Hull, 802s don't work the South Trans Pennine, and trains aren't formed of single 185s (except for the two stopping services Leeds to Huddersfield and Huddersfield to Manchester, for which three coach units are adequate).
It also reduces the likelihood of the 802s and locomotive hauled trains working services where there are very large numbers of people making short journeys, as they suffer from excessive station dwell times where this happens. It will still happen, however, especially between Warrington Central and Manchester Piccadilly with four intermediate stops, and between Sheffield and Doncaster with one intermediate stop. It will also happen between Huddersfield and Leeds, but I don't know without looking it up which trains will make an intermediate stop at Dewsbury.
It also reduces Hull - Manchester journey times slightly, reversing the 2018 journey time increases.