Croydon to Shoreditch fare not offered online

Although I would make this journey using a contactless bank card, I am curious to know why the most logical fare is not found by the National Rail app or booking engines.
On brfares.com and on the TVMs at Croydon, there is a Croydon stations to Shoreditch High St via Surrey Quays fare at £6.60 single.
Even the Train Split app says to travel from West Croydon to Shoreditch on the through train needs two tickets: Croydon to Surrey Quays and Surrey Quays to Shoreditch.
The only time Train Split finds the £6.60 fare is for an itinerary of: East Croydon - London Bridge - New Cross Gate - Shoreditch.

Can any experts explain this?

All I can think is that there's something amiss about the way "via Surrey Quays" fares are interpreted.

I can get the fare to show up for a journey via London and Clapham Junction on the National Rail web site by specifying journeys via Surrey Quays, and I can book through from there to the Hull Trains site. If I book a "not via London" fare from West Croydon to Whitechapel, or a "not Underground" one to Cannonbury, it does give the route via Surrey Quays without the detour.

I don't know why it's doing this, though. The published route code definition just says that fares with the "via Surrey Quays" route code have to go through Surrey Quays. There are no easements which I'd expect to be relevant here.

This can sometimes be caused by the via point on the ticket not being a timing point. Hopefully someone will be able to confirm if that is the cause here.

It can be in some cases (although I would hope something has been done to avoid this problem in each case), but it's not an issue here as the direct trains here stop at every station on the route.

There seems to be an error in the electronic data. It says the journey must go via London Group in addition to going via Surrey Quays. I think that explains the interesting routes e.g. via London Bridge.

This seems to have been fixed in the data and the VIA SURREY QUAYS fares are now being offered on itineraries that don't also go via London Group.