Most likely answer is just that BOE doesn’t have a strong product design culture.

But there is another reason why some may prefer standard: due to the instant payment rules banks are not able to hold inbound payments for screening so if a payment trips a flip that requires screening then it will be rejected. Other payment rails will typically result in the payment being held for a manual review where it will be released shortly later. Instant payments will be rejected if not crediting the recipient in a few seconds.

As this disproportionately affects people with names in common with sanctions lists, to send money to/from those people sometimes a standard transfer is the only option.