This is Mexican standoff. The only "value" crypto assets have comes from exchanges that will trade them for fiat. If crypto holders stop trusting exchanges and pull all their assets that will cause the exchanges to fail and those assets will then be worth nothing. On the other side if exchanges try to earn the trust of holders by becoming "fully transparent" it will be revealed that there's not nearly enough fiat reserves to support the current valuations. (It does no good for Binance to prove they have a reserve of $18B of Tether to back the $18BN BUSD marketcap if turns out Tether is actually mostly backed by Bitcoin that only has a USD value because it can be traded for BUSD...)