Because, there is no incentive for the bank to do that otherwise. The bank does not magically have money, it gets the money from people promising them a return, gives the very same to the young couple for the higher return, and keeps the difference for itself. So, the investors have the incentive to make money, the bank has the incentive to make money, and the young couple owes all that money to the people and the bank, but gets their apartment and have a place to live.
The long story short, it came from the way the previous aristocrats used to pay for all the goods and service in the cities: the beautiful ball dresses, the high-end wine cellars etc. They paid with what was called а "promissory note" (вексель) which specified an obligation payment but could not be produced immediately because the crop haven't yet grown on the fields which belonged to that aristocrat and wasn't yet sold on the market, therefore that note was just a promise to pay. Due to the fact that the aristocrat's daughter need the ball dress by the next Saturday and couldn't wait until the crop will be sold next year the aristocrats needed to present some kind of incentive to those who tailored the dress, so they said "please wait a couple of months and you'll get a bigger amount of the legal tender than you ask for it". The dress-makers agreed to wait. That what is known today as the interest (=the incentive). Back to our aristocrat, the several months had passed, but the amount of crop was still not sufficient to cover for the dress. But the dress-maker needs to pay the workers right now. So he goes to another guy with money and says: "here's a promise note I got from that aristocrat; I would agree if you pay me less money (sic! -> inflation!) than he promised, but I need that money right now; however, once the aristocrat has enough crop to sell, you will get more money than you give me, because you'll earn the interest from the aristocrat and the inflation difference from me". So, those guys with money also have strong incentives to collect the aristocrat notes for long time, and then come to them with the demand to pay right now. So, if the aristocrat was lucky enough to pay those notes at the years of good crop yield he would be ok, otherwise he would have to give up some of his property, typically a village or two to cover for his promises. So, later on the entire governments did the same thing: they need weapons right now or they would loose the power, so they issue their promising notes to pay for the weapon once they win the war and get their adversaries' property. At that point, the legal tender could be whatever, it didn't really matter - the more golden the better. However, it was quickly discovered that when the government needs the legal tender the most - during the war - the population becomes afraid that something will not work out right and they start saving and not spending (=hoarding) their legal golden tender, so the amount of legal tender in the country becomes less and less creating an unhealthy demand for the tender and thus raising its value above what it's actually worth. So those who use the services of the people - the government becomes paralyzed money-wise - it can't pay those in service in legal tender because it's scarce and very expensive for the government to produce. So, at that point the governments started to issue the promising notes (=the State Bank notes) directly to the people in promise to pay them more once they have the money. But if one person (the money guy) gets that 'government promise' from another guy (the dress-maker) even for the real goods and services it's still just a promise so it has less value as soon as it changes hands. And what is the government promise exactly? In addition to the crop grown in the government fields, that is someone in our country would always agree to give you some goods or some services in exchange for those 'promise notes' and bring you the same value you spent giving up your goods and services. On the other hand, how real that promise actually is? If I borrow $10 from you and say I'll give you $15 in return you might believe me because I'm your governmentand you have no choice, but if I ask to borrow $100,000,000,000,000,000,000,000,000,000,000 and promise to return $150,000,000,000,000,000,000,000,000,000,000 you can ask a very legitimate question - where would those $50,000,000,000,000,000,000,000,000,000,000 come from? So, if you see the economy is good, people are working (=producing lots of goods and services) you can believe that government and otherwise (just to be on the safer side) you would demand MORE 'promising notes' in exchange for your goods and services just in case some of those promises wouldn't work out. That is another source of inflation. Moving those considerations into the international arena (because some dress-makers are just better than the others) creates a very complex system with the interest and the inflation in the heart of it. I hope I answered your question. Phew!![]()