Perhaps the only reason a hedge fund hasn't tried this yet is the unclear legal status of doing so. One law blog (https://restislaw.com/liability-51-attacks-cf

Perhaps the only reason a hedge fund hasn't tried this yet is the unclear legal status of doing so. One law blog (https://restislaw.com/liability-51-attacks-cfaa/ https://restislaw.com/liability-51-attacks-cfaa/) argues that a 51% attack would violate the Computer Fraud and Abuse Act, but that blog does not take into account the recent Supreme Court decision limiting its application. It might also be considered market manipulation to take out a short position on a bitcoin-linked fund or company (like Microstrategy) and then take actions with the intention of changing the price of Bitcoin. That could add enough legal risk to make a hedge fund think twice. I doubt a hedge fund could build a sufficient short position on unregulated DeFi networks, either, especially since blowing up Bitcoin would likely break the peg on at least Tether. Still, this would seem to leave Bitcoin in an uncomfortable spot: the only reason the "free from government" currency continues to exist may be regulations by those selfsame governments.