Put an ex-civil servant with no retail experience in charge of a retail operation and see what happens.... Can't recall when I last bought anything from either Waitrose or John Lewis. I did have a charge (not credit) card with them decades ago, but must have binned it at some point or maybe it was cancelled when they switched to credit cards.
Using NewDay was a very strange choice. NewDay are essentially a sub-prime lender and notorious for their lousy systems and rotten customer support. Until recently I had a ND Amazon Platinum card, which did generate decent cashback on Amazon purchases, but they were sacked by Amazon a few months ago so I closed the account. I have a few other credit cards that I use for cashback, vouchers and free forex, and my limits on those are typically £15K/card. By contrast ND gave me a limit of £1.5K. Not a problem but indicative of their business model. I have always paid off my cards in full each month and that doesn't make any money for a firm like ND, which gets its income from those permanently in debt and paying 30% interest.
John Lewis does seem to have completely lost its way. BTL comments about their stores are scathing. And an intelligent 10 year old boy could have told them that there would be problems hooking up with a scumbag operation like ND.