I’m not sure why either, but if you peruse the documents (Item #34), you will see that the city does not have to pay anything, BUT, it is a lot like your parents co-signing on a loan for your first car. If you FAIL to make payments on that loan, well guess what?
It’s still a bit confusing to me, but I still don’t understand why they don’t just go to a bank? Seems they are using our credit rating and bond borrowing status to get themselves a discount. Wouldn’t it be nice if we could get a mortgage with the city as a co-signor?