I think just more lenders realising the value of BTC as collateral and how easy it is to make loans against it (can do it all online and even without having to know the identity of the debtor or check their credit worthiness). And once they realise this, them looking at how good the returns presently are as a creditor. Right now as a lender you can get 15% p.a. and up for loaning out USD, basically risk free.

Competition between a greater number of lenders should then start bringing those interest rates down to where it's still an attractive return but not as high as presently.