Passions change. Also, I'd guess most CS grads going to work for JS aren't passionate about stock trading/market arbitrage - they're passionate about the pay or maybe OCaml, but the actual thing that JS does, probably not - it seems hard to be passionate about in and of itself (would someone work there for free because they were having so much fun?). And even if someone might be initially, they likely won't be after 5 years and enough money to retire on comfortably.