How does it work? In my country (at least non-regional trains) the ticket price is calculated as ax+b where b is a constant price and x is the distance in kilometers. So splitting the ticket is always more expensive than buying two separate ones (but there are other reasons to do it, for example it's a trick to use when there's not enough seats to ride a->c directly - but that's an edge case)
Ticketing on the UK train network is completely inscrutable.
Perhaps the A->C ticket entitles you to travel on either an air-conditioned nonstop high speed train, or a slower train that stops a lot along the way, and buying A->B and B->C tickets you can only travel on the slow train and that's cheaper.
Perhaps all the discount advanced-booking tickets leaving A have sold, mostly to people only doing A->B, and when you look up B->C there are discount advanced booking tickets still available.
Perhaps you depart A during peak hours and so pay a peak fare, but as the B->C portion of the journey starts later, it doesn't fall into peak travel hours.
The UK is also relatively unique in extending full passenger rights even to split tickets as long as you adhere to the usual minimum connection times. (Apparently not out of the goodness of the train operating companies, though, but rather some interpretation of UK contract and customer protection laws which seem to demand equal treatment even for separately bought tickets.)
How does it work? In my country (at least non-regional trains) the ticket price is calculated as ax+b where b is a constant price and x is the distance in kilometers. So splitting the ticket is always more expensive than buying two separate ones (but there are other reasons to do it, for example it's a trick to use when there's not enough seats to ride a->c directly - but that's an edge case)
Ticketing on the UK train network is completely inscrutable.
Perhaps the A->C ticket entitles you to travel on either an air-conditioned nonstop high speed train, or a slower train that stops a lot along the way, and buying A->B and B->C tickets you can only travel on the slow train and that's cheaper.
Perhaps all the discount advanced-booking tickets leaving A have sold, mostly to people only doing A->B, and when you look up B->C there are discount advanced booking tickets still available.
Perhaps you depart A during peak hours and so pay a peak fare, but as the B->C portion of the journey starts later, it doesn't fall into peak travel hours.
The UK is also relatively unique in extending full passenger rights even to split tickets as long as you adhere to the usual minimum connection times. (Apparently not out of the goodness of the train operating companies, though, but rather some interpretation of UK contract and customer protection laws which seem to demand equal treatment even for separately bought tickets.)