Originally Posted by gomestar
maybe they want to be traders
I feel like it's usually the other way.
The prop traders use it to escape from trading. Trading that way teaches you absolutely zero skills except for how to trade (which is why a lot of the floor traders didn't used to be dudes from top schools...and often still are athletes with a competitive element and quick "go left or go right" style decision making). I know that my friends who went straight in to trading have learned little besides how to sit behind 7 monitors while clicking buttons. They don't have work that can follow them home and they aren't used to working on projects--basically it is production line style work. Instead of clocking in, they wait for the market to open, and hammer out their strategies until the bell rings.
Going in for an MBA (with an internship sandwiched in the middle) helps you move into a traditional job since it gets you back to writing, working with ideas, and focusing on things that take days or weeks of effort (and often team effort) to complete.