for a large number of reasons it's hella hard to make money in finance. you can make whatever the vanguard index fund makes "for free" in your pajamas, so in order to justify your existence as an org within a financial institution you're going to need to put together some returns that are, obviously, way higher than that. so out come things like leverage and derivatives (=> hyper-leverage).

and yeah, there are failures, and they lose their shirts, and the beat goes on. but you're probably not going to make very much money (=> last very long) if your rate of return is the same order of magnitude as the collateral you're taking out. it's just not worth it from the POV of the bank.