As well as cost I also heard that it was to avoid the boot up time of the software on the DMI on turnaround. Takes a good 4 or 5 minutes to get fully setup on ERTMS, little quicker if your in unfitted mode, but still a lot longer than a non-ertms unit.
On the subject of ERTMS units, I have heard today that there is ERTMS testing booked on the Cambrian for 9th of March with proving runs in April/May. Entry into service on the Cambrian is dated for December 2025.
Also previously it had been reported that Llanbedr, Tygwyn and Abererch (all short platforms with level crossings and a drivers white light) were going to be a problem with the 197's and were potentially looked at being closed but now it is being reported that they are all in within spec. Llanbedr is apparently still reported to be getting a new platform which is deeper so that the shelter is moved back to aid with drivers sighting the road as the crossing is the last open crossing on the Cambrian and receives a fair amount of misuse, but it is also said that it will be receiving barriers. I don't know for sure but I do hope the platform length is extended so that it fits a 2 car, I think a 4 car would be a bit overkill but would be nice for when the 4 cars are in operation.