Even though you have paid out btc in campaigns (havent got the chance to go through and confirm this), this still carries risk that the lender may want to mitigate since the BTC value may go up in the next 2 months. If it does, or if it spiral out of control like it did last year, you probably wont be able to pay that amount back and would likely default. Its not the same as handling btc for campaigns since with this loan youre likely going to convert it to USD, gamble, buy or pay bills, etc (not saying youre going to do these things but just listing examples) while with campaigns, youre just holding on and paying out btc and not converting it to another currency or using it for other means. Providing collateral allows the lender to mitigate the risk. If they agree to tie the amount to USD, then that would be a different story, but most lenders try not to have it tied to USD.