MMA started out as a free for all and got destroyed by BJJ. Then Muay Thai was brought into the mix + BJJ to dominate year 5-15 (approx). And for the past 10+ years, it's been dominantly Boxing + Wrestling with BJJ & MT dropping down to secondary arts.
These many other ways of fighting had their chances in years 1-5 (esp. year 1) when it was potluck, bullshido, anything goes almost; where you can write down as many Black Belt degrees and fake & real fight experience as you wanted on the registration and Bruce Buffer woulda announced it.
So what happened to all these other ways of fighting? They've laying low for the past 25 years, just waiting for the right moment to strike and bring home all the $$$ and glory to their style?