Does anyone know what the explanation for this is?

The journey options with no ticket radio buttons are via Ely and Birmingham, the others all via Cambridge and London. There are no single tickets available on the cross country route either.
What's the point in displaying the itinerary for a route option if it can't sell me a ticket for it?
Not that's I'd go for 5 and a half hours on a rammed XC 170, but I'm curious!

The journey options with no ticket radio buttons are via Ely and Birmingham, the others all via Cambridge and London. There are no single tickets available on the cross country route either.
What's the point in displaying the itinerary for a route option if it can't sell me a ticket for it?
Not that's I'd go for 5 and a half hours on a rammed XC 170, but I'm curious!