I don't know enough about the legal implications of this, but I doesn't say investors are walking away because of this. It sounds like the same sort of thing they have at Chelsea.
Chelsea fans own the ground, the club can't move without permission from the owners of the ground.
It sounds to me like if FSG wanted to sell up, the fans would have first refusal on an option to buy the ground. I don't know if it's when FSG sell the club as a whole or if they tried to sell just Anfield (to relocate)