Taxi Cheaper than Trains?

It is cheaper for four people to go from High Wycombe Train Station to Marylabone train station by Taxi than by train.

A single trip from high Wycombe costs £16.50 for one person.  By Uber it costs about £40 on average but the car has room for four passengers! If there were four passengers they would only pay £10 each. 

This info is based on my own observations and access to my Uber App. I believe this is true of many other stations.