I don't think you can compare the budgets of the everglades challenge or the R2AK to the FL300.
From some quick numbers online
Evergaldes Challenge $395 a person, 119 entries = $47,500
R2AK $620 team + $20 a person, 40 teams = > $24,800
FL 300 $395 a team, 15 teams =$5,295
I also ready plenty of feedback online that the fee shouls be lower still....
That says it all right there.
And I disagree that the WaterTribe challenges do better PR...most of that is generated from the sheer number of participants that post stuff. A couple dedicated volunteers keep the Facebook page updated as the race progresses but there's not some big push by race management to drive a huge PR campaign.