People who live in Bucks or Herts do not have a say in London politics, and when service changes are proposed this is often noticed. You no longer get off-peak semi-fasts to/from Amersham, and you no longer get as many peak fasts to/from Amersham, because it was better for London ratepayers in places like Pinner to have everything run all stops. Obviously the cancellation of the Croxley link is the biggest example of how handing control to TfL really doesn't benefit people who live outside the London boundary. Put simply, Bucks and Herts residents don't pay so don't get a say.
The integrated fares scheme came in a long time ago, with Travelcard and Capitalcard, as
@A0wen also says. My season ticket from Hemel Hempstead- not as far out as Aylesbury- included all-zones London travel. Sure, it was on a piece of orange cardboard and not a piece of blue plastic, but that's about medium not utility.
As a relatively regular user of the trains out to Amersham (t'missus worked there at the hospital, and the restaurants were better in Amersham than Hemel for after-work dining!) the main thing that needs sorting is the under-capacity of the Chiltern trains. Even the ones that were first stop Amersham were rammed, possibly because they were first stop Amersham and so much quicker. But I don't think switching the Chiltern trrains to Met trains is the solution, the solution is to get some bigger trains for Chiltern and move the 2-car and 3-car 165/166s to the provinces where their size is better suited.