Why not hedge with cheap etfs instead of a hedge fund?

I've seen dozens of posts and articles saying that hedge funds exist because they can deliver positive returns regardless of the market. That makes them attractive for things like pension funds where the goal is to avoid losing money. Understood. But why can't that be done with cheap etfs? Why don't pensions invest in a treasury bill etf if they need fixed income? That's what retired people do. Is the idea that there are hedge funds that pensions invest in that have higher returns but still no risk? In that case, why not offer the hedge fund to the public?