So lets take 10k for example
Guy X don't have any tc, so you lend him 10k, if he doubles his money he will get 2500 tc extra if he looses his money he have to pay back 10k. If its a random guy the odds of him doubling his money is 50/50, but if he wins that 50/50 chance he will only get 2500 tc
So why would anyone that doesn't have 10k take a loan with a 25% chance of profit, and on top of that you expect that guy if he looses to pay you back tc he didn't have in the first place.