The problem is that the deregulated bus network is just not attractive enough for a local planning authority to sink millions of pounds of Community Infrastructure Levy from new housing developments into, nor would it deliver the modal shift that would be required to make the transport case work for a massive increase in new homes in the area. If it were a regulated system like TfL then a step change in the attractiveness of the bus system could tempt some motorists out of their cars but probably not enough to avoid gridlock on the local road network. You can only build that number of new homes without costly improvements to the local road network if you can keep car use down. Very few local authorities want to start a road building programme.
Harlow Town station is not exactly well located for most of the town (was the New Town sited due to where the county boundary is ?) but extending the Central Line there would be a very expensive way of only slightly ameliorating the situation. As mentioned, no-one would ever use the Central Line to get from Harlow to London, and I doubt the traffic flow to Epping is sufficient.
Bus services can be started up, modified, withdrawn a whole lot more easily and cheaply than rail with all its associated infrastructure.I doubt it would pass the cost benefit ratio analysis, that was the cause of the Met extension to Watford Jcn failing, when it transpired that the actual costs associated with the project were at least double the original estimate, it failed the cost benefit ratio analysis too.
Harlow's addition to London Underground proposed by council
A town's planners want to see the Central Line extended further into the county.
www.bbc.co.uk
OK maybe worth some safeguarding in expectation of some great Section 106/ Community Infrastructure Levy payments, in due course. Metroland (or Centraland?) trumping Green Belt and NIMBYs? Unlikely.
Densification of Harlow, Epping, Ongar, Roding Valley first?! https://londonist.com/london/features/least-busy-underground-station-roding-valley.