There might be a few relatively untapped markets left, but for the most part yes. It already peaked in the US in like 2009. Brazil, Japan, UK, Canada, Russia - all peaked at various points.
It makes more money now because of the sheer amount of events, the crazy tv deals that live sports get offered nowadays to try and keep tv alive, price hikes for PPV and tickets etc. Its super corporate now and designed to milk the maximum amount of money possible, but the actual interest in events isnt any bigger than it was 15 or so years ago.