I believe its to do with how the cash distribution hubs handle coinage.
As there is so much "good" coinage, much of it is re-bagged and recirculated, rather than bags of new coins being issued. Pretty much every bank and PO I've asked in has all said the same - they get sealed bags of recycled coins, and none so far have admitted even handling any new 10p's. With the rise of contactless, there is much less active coinage, so it becomes less likely to see new coins until long after their minting date.
Some is definitely creeping out, but the general feeling is that those who find the bags of magic coins (PO workers etc) might be the ones saving it for family and friends, rather than it all reaching joe public.