There is a recurring theme of governments and citizenry becoming excessively indebted.

There are probably numerous reasons, but the two basic reasons are:

1. Where fractional reserve lending is allowed, it is a very lucrative industry for banks and lending institutions. Even though there are operating costs, by using fractional reserves the bulk of the "money" lent out is created out of nothing so the cost of the raw material is nothing. Kind of on the idea if a person had to "borrow" air or water and pay interest on its use. The ones producing the air and water to "loan" might have some costs associated with the business, but their raw materials would be free. So fractional reserve banking by its nature tends to be a very lucrative business to be in. Therefore there is always a very vocal voice of those involved to promote and legislate laws conducive to maintaining a fractional reserve banking industry. Once the banking industry is in place, of course it is always going to be encouraging people to use it. It makes the owners of the banks very wealthy to do so.

2. Governments are always prone to spend more money than they are willing or able to tax the constituents. The government might run surplus for a while, but there always comes perceived a need to spend more, be it on a war that needs to be fought or a social program to be created that citizens are unwilling to fund through taxes. And the banking system is all too willing and able to create the money from nothing for the government to spend more, with a mere promise that the cost will be borne by future taxpayers. If a war was waged and people were immediately ask to put up the funds to support it, there would be revolt. But borrow the money and debase the rest of the currency is a tax that few people understand and the effects are more gradual so mostly go unnoticed. Governments can print money directly to fund excessive spending (direct monetization) and simply debase the currency. But sometimes the citizens are against this as some understand that the mechanism is a hidden tax. Or a government can pretend the borrowing is only temporary and will be paid back when the economy gets "better" and borrow the money from an all to complicit banking system.

Those are the two basics that reoccur throughout history. Of course it is not hard to convince people to spend now and pay later. Especially if it is presented that there is no pain involved, only pleasure. But like a drug addiction, the user tends to need larger and larger "fixes" till it ultimately ends up as the demise of the user. Such is debt when it is not very carefully controlled and limited.

There are other ways of controlling debt. Debt, based on borrowing from real capital sources to finance productive enterprises, is a good thing. Excessive debt based on creating money from nothing and loaning it out leads to credit booms that cause malinvestments and over production that ultimately leads to a debt that can not be serviced and resulting bust.

When money is created out of nothing via fractional reserve lending, more money is created than can ever be repaid because while the newly created money eventually goes away when repaid, the interest portion of the debt does not and has to come from original base money. So by the inherent design of fractional reserve, as the money supply expands the interest portion has to be paid by additional expansion of the money supply. Unless more base money is created to satisfy this interest burden (thereby debasing the value of the money), eventually all the original base money is eaten up in interest payments and then the interest payments have to come from additional fractional reserve lending. Debt paying off debt. The system eventually self destructs in a spiral of more debt needed to support existing debt.

Others can probably give a better, more clear, explanation.

John