This is precisely my point. 20 years ago, a train was slow and therefore not well used, so it is never worth trying again now we are in another era. Even with an airport with 10m more passengers, flying more frequently themselves (Gatwick airline/flight profiles) and more employees. Or population growth of several hundred thousand across Kent, Surrey, Sussex. Or where a 1 hour train ride can now be productive, or easier with kids, or less boring.
And with a different branding, stopping pattern, publicity... the main line straightness (and quietness) are really an asset, used well. etc etc etc - why explore anything?