Walk into any large bank and ask how a customer is verified. You will get a different answer from each product line. Each is correct. None of them is consistent.
Why consistency loses to local optimisation
Each team optimises its own KPI. Each builds its own variant. Years later, the bank has nine ways to do one thing.
What a shared execution layer enforces
The same policy, the same evidence, the same audit trail — independent of the channel or the product.