If not, the cost would need to be accommodated where the interest's been lost. I don't see a net cost reduction.
Perhaps there's a welfare effect, I don't know; living where cards, phones (QR code or NFC) or bank card (NFC) are all accepted and have been for several years, most passengers still opt for transport card but a non small amount prefer phone but that's my completely localised anecdote.
Would costs be increased through transaction or implementation fees for capital not yet depreciated? Implementation doesn't need to mean new hardware either, it includes tooling, software, but goes beyond to different workflows needing testing from fumbling for phones vs fumbling for cards to customer support - were the results from the trial run you mentioned published? Is there any compelling urgency?