Bitcoins credit can exist just fine. I've made loans, and received loans, both with interest, and both paid back. Guess what... it worked!
But why on earth would anyone borrow Bitcoins at present when you can get a Fiat loan for interest that's lower than inflation?
A Bitcoin loan otoh carries a significant risk of Bitcoin gaining significant value and a default as a consequence.
At some point, when bitcoin is more mainstream, this will change, of course.