You need to consider what work and, more generally, what society is. Society is fundamentally a group of people working together to satisfy each others needs and wants. Work, or productivity, is making progress towards this goal and is something we tend to reward with money, though not always.
I think a fair analogy for society's productivity is a grocery store. Imagine there was a grocery store, the only grocery store in existence that also happened to be the only way to get food. Everybody would come in and take whatever they needed, but you didn't necessarily have to pay. If only some people don't pay this isn't that big a deal - the grocery store as a whole eats the losses but continues working more or less fine. And for those that simply cannot pay at all, well - there's not really any other option. But then there are those that could pay, but for whatever reason, do not. If enough people did this - the store would eventually go out of business as it would not be making enough to sustain itself. If everybody just did as they want, society would collapse.
More generally here money is an indicator of how much you've contributed to society. People look at disbelief at how much Jeff Bezos is worth, yet somehow think nothing of how much Amazon has completely revolutionized the world of purchasing things as well as brought prices to lower than ever levels. The reason he's worth as much as he is is because he has contributed immensely to society.
Of course the system isn't ideal and some people manage to make enormous amounts of money while contributing next to nothing to society - people who deal with finance are the prototypical example here. And similarly there are also people that contribute immensely to society, yet never see much in the way of reward from it. Herman Melville is now seen as one of the more important individuals in our literary history, yet received no recognition during his life and died without his work ever really being recognized, let alone rewarded.
Yet for all of its flaws, our system does generally do a good job of creating a system where people who contribute to society are rewarded which creates a strong incentive system to contribute to society, even if only to make yourself rich in the process.