Money is part of human nature

As much as it pains to admit it, the concept of money is — to the extent that you can define the term — entirely natural for the human animal. If it didn't exist, someone would have to invent it. Even in prisons, where money is prohibited, people still reinvent money (witness actual use of cigarettes and tuna cans in the premises).

Humans aren't the only species who would invent money either — the use of money has happened even in nonhuman animals:

Why would anyone invent money, though? Isn't money the root of all evil?

No. Once we understand that money for what it actually is — a token of delayed gratitude / fulfilment / pleasure — it's obvious that it would need to be invented once again, and again, and again. We need a way to account for gratitude, because gratitude is part of the human experience — as it is for many nonhuman animals too. Money fulfills that purpose.