Oh, we don't have a monopoly on producing and commending them, NT.

I suspect that the blame for the majority of the pieces mentioned here to which you refer can be placed elsewhere. (Sorry for the Yoda-speak in that last sentence; it's late.) Seriously though, I have generally found that SSG-led parish music is much more catholic, both in spirit and range, than that in most other parishes. We also know and accept, for example, that folk music will change for the reasons discussed above, but that, on the other hand, with the chant there is not to be any monkeying about.
However, on that last point, I learned most of my chant from the 1933 edition of the English Hymnal; i.e. in the Sarum versions. To be honest, I prefer them. Even now, nearly 50 years on, I still get them 'wrong' from time to time. Presumably the Sarum and the Roman versions represent just two different codifications, at different times and in different places, of the same chant melodies which had developed differently?
Come to think of it, I wouldn't be surprised if many members of the Ordinariate, originating, like me, from the Anglo-Catholic branch of the Anglican Communion (where the English Hymnal still holds sway - albeit in a new and, IMHO, greatly inferior edition), continue to confuse Salisbury and Rome.