Simple answer:
A successful founder will sell 1 (maybe 2) companies in their lifetime, while PE/VC firms do these deals every day of the week.
It's like entering the ring with a pro MMA fighter and expecting to have a fair fight. You have a massive disadvantage that can't be overcome. The best you can do is take precautions and "do your best" but "your best" and "precautions" still isn't good enough if your opponent really wants to screw you over. Unfortunately this happens all the time in VC, and especially in PE.
As an example, when you sign a term sheet to sell a company, most founders assume the deal will go through at the price that was agreed. In reality, deals almost never close at the originally agreed upon price. The buyer usually waits until the very last minute, then drops the bomb on the seller "Btw, we can't do the deal anymore at this price, but we can sign tomorrow for 30% less". The sad part is it's such a common tactic and PE firms will do things like encourage founders to get their whole team excited about the transaction -before- dropping the bomb / new deal terms. At which point the founder is basically trapped with their whole team excited about an exit, which PE then exploits.
All of the lawyers in the world won't help if the PE/VC firm has the ability to spread the word "Don't do business with John Appleseed" effectively shadow-banning you from future funding from anyone. PE/VC world is very small and they have a lot of political leverage, which almost always trumps any legal leverage a founder might have.
The best defense is to have another VC/PE on your side.
That also puts bootsrapped companies at a severe disadvantage (no VC fighting on their side for the best outcome). There literally are PE firms who specialize in buying "family run bootstrapped businesses". Why? Because they're the easiest to screw over and exploit.