That I understand. Like church ladies in charge of the piano.
My guess--and I think it is more than a guess--is that the Trinity Psalter offer (which in no way was to replace the Trinity Hymnal) had to be accepted by our ultra-professional music director/organist/pianist/quire leader and an etc. or two. He is a traditionalist and has a kind of de facto seniority in all things musical. Most likely he didn't approve the idea. As to one Psalm per week, I assume the preference of the same man was that we should not. Besides we would have to buy something better than the Trinity Hymnal's barely unrecognizable paraphrases. O, I almost forgot. Someone already offered to pay for a Psalter, but even for free the offer was turned down.
'mystifies' was a good word. Here are some adjectives that come to mind:
incomprehensible, unexplainable, unintelligible, unaccountable, strange, puzzling, perplexing, baffling, bewildering, mysterious, insoluble, enigmatic, weird, unfathomable, incredible, unbelievable
It appears that we are EP after all 'Exclusion of Psalmody'