Adding to this, the money to repay bonds has to come from somewhere -- usually taxes. So, if a government issues a bond it is committing to collecting the amount of money for the bond-plus-interest from the populace. It's the government taking out a loan, essentially, on the basis that it can use long term tax revenue for repayment.
Why not just use taxes directly then? Sometimes you need a lot of money for a specific project and it would take too long to collect that money through taxes at a rate that is reasonably payable by the populace over a short enough time frame.
Suppose you need a million dollars to cover the cost of replacing some infrastructure -- like a critical pipeline for your town's drinking water -- but you only have 100 people in your small town. That's $10,000 per person if the cost is split evenly. The people in town may not have that much money to pay all at once, but getting the pipe fixed so they have water to drink is really important. So, the government gets a loan (i.e. issues a bond) and pays out the amount plus interest over a long period of time. Adding 5% interest and breaking the payments up over a 30 year term would require everyone in that hypothetical town to need to pay about $30/mo more in taxes to cover the cost. That's probably a lot more politically feasible to actually collect than trying to get everyone to pitch in $10k right now.
There's also a 27th (non-alphabetical) "ending" that's quite different from all the others. I think it was originally part of a DLC but it just came with the version on Steam when I played the game ~5 years ago.