...people have lost the desire the flame has gone out and only the hardcore are left. It's just too hard for those people and there out of the system now and will take something exceptional to bring them back.
For all the reasons people drop out, that is very true - once you lose someone, they are generally harder to entice than newbies.
I've lost track of the number of people I've spoken to, who got the shits over something (trivial or significant), and walked away.
Mostly, those people seem to draw a line under it, and won't come back even when you explain how that problem doesn't exist anymore.
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The track location stuff is probably significant.
Personally, it is MUCH easier for me to go racing if it is a day trip - as soon as the event requires me to be away for a night, it all becomes considerably harder to get a leave pass.
Two nights away becomes a major operation, one way or another - and is a big part of why I've dramatically reduced the number of Heaven events I've done in the last few years (not a criticism, just an observation).