> If you put BTC as collateral to get also BTC, then why don't you just save slowly by yourself until you get the amount you need and done. No need for anything else.

True. Saving is better than borrowing. And therefore software for saving bitcoin is better than software for borrowing bitcoin. But there's lots of software for saving bitcoin; there's hardly any software for borrowing bitcoin, except altcoin software. So there's a gap and I want to fill it.