They are not betting against it, its a "hedge:. They are using it like insurance, or placing a bet to protect yourself.
It will help smooth out the wild swings in price, so you wont see it rise or fall a thousand dollars a day as much. It will still happen, but less and less over time.
There are many Wall Street Fund Managers that are not allowed by regulations to buy bitcoin,but now will b e able to. It could be $10 or 20 Billion, or it could be a LOT more. If the market cap adds 20B, a bitcoin could add another $2-3000 to the price of a bitcoin very quickly, and that on top of the money that's streaming in now.
And still less than a percent of the world involved, so with a 250B market cap today, has a long way and ltos of opportunity to catch up to gold with an 8 Trillion dollar market cap. This could still be a ground floor for long time.