Why is it so essential to have modern rolling stock running TransPennine services?
Several reasons
1, Door position on the 185's allows for shorter platform dwell times
2, Performance of new power units vs old
3, TPE is marketed as a premium service to encourage intermediate distance travellers to transfer from car to rail - which has been successful
4, 15x type units don't get refurbished to a higher standard as a new unit, the travelling passengers aren't stupid enough to accept the nonsense peddled about refurbishment when it's the same train with a new fabric cover and new carpets
5, 15x aren't compliant with 2020 standards for disabilities in terms of such fundamentals as passenger displays and toilets
6, 15x can't go on forever and will at some point need to be replaced, starting early with the 185 was a positive step along that line
7, New trains allow higher fares (good for the TOC)
8, A large single consistent fleet makes for less troublesome fleet management at the start/end of each day and makes maintenance seamless as oddball larger units don't create operational gaps in your service when missing
9, insert one of 100 other reasons I've not thought about