The whole basis of the Parkway station (opened in Nov 2001 on the same day as the new terminal) was that for no more than the price of the train ticket, you would arrive directly at the check-in desk ... just as you can do at Heathrow, Gatwick and Stansted .. and a variety of others.
The inconvenience and time wasted by having to also use the shuttle bus (with the further risk to getting to easyJet's check-in before it closes in your face) should make the train ticket cheaper as an apology.
Of course it doesn't take long for the principles to change and pledges to be forgotten if there is a quick buck to be made.
Personally my journey to work from Redhill to St Pancras is by Southern Trains and tube and I avoid like the plague the FCC trains (which would be equally convenient) but which I consider as cattle trucks without the straw.
I really fail to understand how the airport management avoid noticing the obvious, in that the perceived easiest and cheapest will get the business and the others will fall by the way. Those perceived to be cynically lining their pockets will become victims first.