I do think there is a large connection between grade performance/SAT scores and general aptitude and success later in life. But as you said there are plenty of circumstances that would lead to poor grades that aren't related to ability - but I would also say those circumstances are also possible indicators of how good of an employee you will be. For example having behavioral problems as a kid could lead to bad grades despite otherwise capable of good grades, and I would suspect there's connection between childhood behavioral problems and conduct as an adult.
I've worked for one of these businesses before - basically staffing a daycare running a very compelling roleplay scenario so a millionaire/billionaire has an excuse to get away from their family for 10 hours a day. It works best if you're a fresh grad college kid who doesn't realize any of that for a few years and is just glad to have gotten a job.
So, the actual intent of all of their hiring circus is to ensure they don't accidentally hire someone who realizes what's going on.