You just have to accept thay in a developed and wealthy country like Britain, having a family car is a norm, and the costs of it are somewhat incidental. Yes, you can account things in such a way to make a rail trip seem cheaper, these commonly leave lots of things out, like getting to/from the railway, but it's one of those things that is normal to have.
Sure, life would be cheaper if you didn't get married, but most do. If you didn't have such a nice house, but most strive to do so. I do accept that members of this board are something of an outlier when it comes to transport decisions, but for most of the population, if they are not going to or within London, they hardly ever use a train.