I left my bag on a train – why must I pay £24 to get it back?

The rail operator refused to send it back by train and insists on using an expensive courierTravelling from Birmingham to Bristol, I left my overnight bag on the train. I reported it to the train operator (CrossCountry) and station owner (GWR) and was told by both it would likely end up in Bristol. After two weeks it arrived at Birmingham New Street where lost property is managed by the Excess Baggage Company. I have to pay a £24 courier fee plus £5 admin. Why can’t it just be