It would be very ill-advised for someone to take out a loan in BTC if their income is not at least somewhat tied to BTC.
Anyone who does not have a steady stream of Bitcoin income that tries to take out a Bitcoin loan had the intention of defaulting/scamming from the start. There's simply no good reason to take loans in Bitcoin unless you're working with Bitcoin - and of course, Bitcoin is extremely appealing to scammers as well.
Not necessarily. They could be expecting to receive BTC that is not income in the near future, for example, they recently purchased BTC via coinbase, but wants to make a purchase before coinbase makes the BTC available. A borrower could also simply be taking the risk of having to repay their loan at a higher BTC price, however as mentioned above, this is not a good idea on the part of the borrower
Services like Bitbond supposedly offering 13% interest per year are extremely stupid considering that the Bitcoin price has basically doubled in the past year. People who do fiat-denominated loans lose money.
Most people's bills are denominated in terms of USD, not BTC, and BTC is a highly speculative asset with a very volatile price, so everyone may not want to bear the risk that the price of BTC will decline. I have made USD based loans in the past and have been happy with the results....I am also a large swap provider (lender) on bitfinex, and have been happy with the results, especially recently.
The problem with sites like Bitbond, and BTCjam are the high rates of fraud and identity theft, and at least on the part of BTCjam (I am unsure about Bitbond), the very inefficient method of getting judgement against defaulted borrowers -- lenders will need to individually pursue judgment as owners of the Note, as opposed to BTCjam getting judgment as servicer for owners of the Note, and if someone makes $25 or $100 investments in individual notes, this will not be cost efficient.