Splitting up bigly hyped final seasons also lets cable channels schedule re-trans fees negotiations with cable carriers over multiple highly rated years. More ratings leverage during negotiations=more money during the agreement period even after the show ends. At least, that's partially what happened with AMC and Mad…

I could be wrong but I'm pretty sure the idol Adam finds is the merge camp idol, right? So it's not so much a late add, as it is a late find. It'd been sitting out there unclaimed for a few votes and would have been removed after that vote. I guess production could have still retrieved the idol earlier in the game…