No fare for the obvious route from West Croydon to Mildmay line stations

I am checking some fares from West Croydon to a number of stations on the Mildmay line, but there are completely no fares on the most obvious Zone 2-5 route, while the corresponding route is the default from East Croydon instead.

For example, the obvious route from West Croydon to Kensal Rise is via Clapham Junction and Willesden Junction, but all the 5 available fares in the fare finder are defined via Zone 1.

In contrast, if the starting station is East Croydon, Waddon or Selhurst, the default is assumed to be via Clapham Junction and Willesden Junction as far as Gospel Oak, and a pink reader route is available until Caledonian Road & Barnsbury.

Why is West Croydon lacking a fare for such an obvious route? If I really want to travel between Croydon and Gospel Oak, the most reasonable option is to change at Clapham Junction.