You can hardly blame TfW. COVID has disrupted everything, more so in Wales than in England (sensibly in my opinion, but that's OT). Trying to predict when anything might get back to any sort of normality is very difficult. Given passenger volumes are going to be well down for months, particularly for the white collar commuter traffic into Cardiff which create the demand that makes these units needed, I'm guessing there is much less of an urgency to get the units into service.
Just because a lot of rail enthusiasts are keen to see a type of unit introduced doesn't mean it's the right thing for TfW to prioritise in the current environment, particularly if it increases risk to the drivers who will need to be trained before they can drive them.
BA has just retired its 747s 4 years early, as have most other airlines, because they no longer need them, so it's the right business decision, even though it's sad. The same is true of the 769s - they are not needed with any degree of urgency, and TfW will base their decisions on need, not sentiment.