It's not even money, really. It's just that organisms that aren't heavily eusocial seem to have this thing for acquiring more resources for themselves to manage some way to stay alive, keep it that way, and attract positive attention, generally at the expense of other considerations. Humans inclusive, on both counts. Consider how 'the competition' is seen as something to do your best to eliminate or at least marginalize. Money is valuable for being a medium of exchange with agreed-upon equivalency, and in the end is no more or less evil than any system, but then consider it's a handy way of denoting access to resources... so in a way, we want more, we're made to want to get more, and money is as good a way as any other as getting access to what we want when we want it. We're all about wanting to have enough of this anomalous 'something' we define as resources which ensures that we will live and live comfortably at that, and money is an easy way to get it and show it.