I'm curious as to why splitting a ticket ends up cheaper than a single through ticket. For example, I work in London once a week and buy a return from Horsham to Farringdon at peak time. This costs £49 for an anytime return. If I ask for the return with a split at Gatwick, it costs £33 despite both portions of the split needing to be anytime. Is there a simple explanation for this? I am aware I have to catch trains which stop at Gatwick, but that isn't an issue as all the trains I could feasibly catch stop at Gatwick.
It's generally because there is often a huge premium charged for longer distance journeys.
Shorter distance journeys may be (or have historically been) set by train companies with a cheaper pricing policy.
In other cases it may be because longer distance day returns were abolished.
For example York to Sheffield is priced by Northern, while Sheffield to Derby is priced by EMR. Both offer day returns and have relatively reasonably priced fares (by GB standards).
But CrossCountry (XC) set York to Derby; they do not want people to buy cheaper
day returns; the through fares are set to be
really expensive (it's considered too far for many people to want to drive, has no viable bus/coach alternative and is far too short obviously for planes, so they have a captive market) and peak restrictions are set to be really onerous, with off peak not kicking in until 0930 onwards.
Under British Rail, York to Derby Saver Single/Return fares were valid at
any time but XC re-named this as "off peak" and require people who travel before 0930 to pay the extortionate Anytime fare.
Savvy passengers know about split ticket websites and use a split ticket provider. Non-savvy passengers may pay whatever XC ask them to pay as there is no viable alternative. This maximises revenue on a yield management basis, with people paying a price that more closely resembles what they are prepared to pay.
Some people are put off travelling and either do not make the journey or use another mode. XC are very happy for some people to make this choice, as at some times of day XC trains are fully loaded and XC have no desire nor easy means to increase capacity.
Therefore XC see the current situation as the best possible scenario to maximise revenue and suppress some demand; why have full trains of people paying lower fares, when they can reduce overcrowding, have savvy people paying the lower fares, and people with big budgets paying really high fares?
If XC reduced the cost of a day return trip on their 0844 departure from £116.20 to match the split fare (around £40) their trains would be even more crowded and they would make less money from those passengers who are prepared to stump up the extra £76.