It's not hard if you make that much, just make $150 million and live like you make $100,000. Invest $74.9 million a year at even just 3% a year makes you a billionaire.
This is true, but I think there's plenty of evidence that Bobby doesn't live like he makes $100k. The private jet alone would be many times more than that.
I don't see how not spending $37 million is hard.