I came across this article recently:
On the face of it, nothing to to with the Uckfield-Lewes line. However one section stands out:
Rail commuting is very important to the East Lancashire economy. The Greater Manchester area is a major economic generator of the whole region, and we need to make sure that people are able to easily travel there from East Lancashire.
Replace 'Greater Manchester' with 'Brighton' and 'East Lancashire' with 'East Sussex'. Currently it is not possible to travel from Crowbororough or Uckfield to Brighton by rail, nor from great swathes of Kent without using circuitous, time-consuming routes via London or St Leonards or Redhill. Brighton is a major regional economic generator.
It is forgotten that before the line closed more passengers from Uckfield travelled south towards Lewes and Brighton than north to London.