Neil Williams wrote:

It is cheaper to operate a bus service than a train service. In a
place like London, these services will operate regardless of which one
a single given passenger chooses. As such, there is no cost directly
attributable to one person's journey, apart from a tiny amount of
extra diesel or electricity and the bit of paper their ticket is
printed on. If they're using Oyster, the latter cost doesn't even
exist.

This was, of course, the same argument recently used against the
person who claimed that it was unreasonable for a journey from zone 6
to zone 6 via zone 1 to cost the same as one from zone 6 to zone 1.
There is no significant directly attributable cost to either of those
journeys. That is the nature of a public transport system.

However, if the fare charged for a Z6 to Z6 journey via Z1 was double
the fare charged for Z6 to Z1 or vice versa, the effect might well be to
reduce demand for the service. In that event, costs could then be saved
by deploying fewer trains and employing fewer staff.

Please note, however, that I am not advocating such a fare regime!

--
John Ray