The gains from moving further out are all priced in through increased cost of public transport, so on top of the lower quality of living and longer commute, you generally end up paying the same.
When I moved out to zone 5 from zone 2 (well technically 3, but my best route was get the bus to a zone 2 station), the combined cost of the premium on my travel card and mortgage/insurance/other costs was still lower than the 2 bedroom flat we used to rent.
The thing is, there is nowhere "cheap" in zone 1 or 2 that people with options want to live in, but once you get further out, you have a lot more choice. I certainly could end up paying more - I'm within a short bus ride from some of the most affluent areas in England (parts of South Croydon is full of large estates that are dirt cheap by London standards, yet within commutable distance to central London).
The quality living for me is far higher here, and the travel distance to central London is low enough that when I need to commute in I often had shorter commute than people who lived in zone 1 or two but happened to live on the "wrong" tube line.