It is not a human trait. It is a property of money. Interest is a bribe to keep money in circulation. There is an incentive to pass this bribe onto someone else. Why is it a property of money? Because money has a liquidity premium versus any other asset and no holding costs. It is rational to ask to be compensated for giving up this liquidity for the face value of money. Money is a payment network that introduces costs for businesses that accept it. Businesses must be close to consumers and open whenever consumers want to spend their money. They must also have a variety of uniform products and if it has to store them it will have to pay for storage costs. Think about it like being an on call employee. You must be ready to respond at any moment and this flexibility is worth a certain amount of money.

Now, you could call the national money system to be a public service provided by the government (and indirectly by private businesses).

If you were to issue your own money what would it's liquidity premium be? It would be very low to be sure because barely anyone accepts it.

So, the holders of money effectively own a free subscription to this public service. If they lend out money, they will obviously charge a fee in proportion to the liquidity premium. This fee is included in the interest rate.

The borrower is now paying for the liquidity premium, the cost has been fully internalized and the problem is gone right?

The problem is that the liquidity premium that is part of the interest rate is erroneously calculated as the cost of capital. It is not, it is the cost of liquidity.

Now, things will get very strange. When the borrower spends his money, he will be obligated to pay the subscription fee, the cost of liquidity, even though he no longer has the money and he is no longer benefiting from the liquidity services. What this means is that the money system constantly screws over people who use money as a medium of exchange and rewards those who sabotage it. It will look as if those who "save" money will be rewarded for their frugality and "moral" behaviour and those who are in debt are being rightly punished for their unsustainable and and "sinful" behaviour.

Now imagine if private households all follow this strategy of selling more than they buy and saving and lending the rest. There must be another sector that earns less than they spend and accumulates debt though borrowing. The government is forced to avoid austerity at all costs. It must become the "immoral sinner" that spends in excess to shield the private sector.

If you want to solve the problem you would have to make buying and lending symmetric. Lending passes the cost of liquidity onto someone else which is in theory ok but only if buying also passes the cost of liquidity onto the seller so that no liquidity premium accrues to the lender. He will pay a liquidity premium and earn liquidity premium which then zeroes. The only one who then collects the liquidity premium is the central bank that issues the money.

The problem with this is that the interest rate on cash would be negative and paper technology isn't advanced enough to calculate and display a dynamically changing face value. It isn't some conspiracy by a cabal, it is actually an engineering problem that originates from our historical and cultural attachment to cash. Humans aren't evil bribe collecting monsters, they are just in a rationality trap that is difficult to escape.