it's very precisely about money.
There's only 4 'power' conferences now and conf championship games (really just 2, tbh).
Even after the first round of a 24-team playoff, where you'll have some blowouts and fringe teams in, you still have 15 games of roughly top-16 competition after that. That's a massive increase % of "big" - ie lucrative games.
These decision-makers would sell their own grandmas for an extra dollar of revenue, so forfeiting 2-4 big conf championship games for 15 big playoff games is an easy financial choice.
Our society wasn't always a whore for an extra dollar. Somewhere along the way, we changed.