Each dollar that you hold and don't spend represents one potential vote for what the economy should do next. If you vote wisely, your votes usually get returned to you. If you vote poorly, they usually don't come back.
Rich people are a form of representative election. Some people give their proxies to others that they think will make wise economic choices. If you choose your proxy well, you also get rewarded with more votes.
That system has led to a situation where a viable equilibrium exists wherein those with unspent money can tend to make choices that benefit mostly themselves rather than the whole economy.
Each spent dollar is a production order. Investment is planning; spending is executing. If you don't spend enough money to execute on the plan, it will fail from a lack of material support. If the plan is good, and the work gets done, everyone benefits. That's not zero-sum. You can get out more than you put in. That's the whole point of having a specialized, productive economy.
But the investment portion of the economy is zero-sum. You can't order more than 100% of the productive economy that exists at any given moment. Every day, one pie the size of the productive economy gets auctioned off in tiny pieces. You can order the productive economy to grow its own capacity a bit, to make bigger pies tomorrow and into the future, but after it does, you will still have to re-vote to use it. Once the investment economy started gambling with itself on which of the candidate economic plans had the best prospects, it turned itself into a realm where someone else has to lose in order for anyone else to win. People stopped voting on bigger pies, and started voting strategically, to get more votes in the future. "Don't make more pie; make more votes!" They forgot that making and eating the daily pie was the important part of the voting process.
As for philanthropy, that might be an attempt to create a standing vote for "let's plan to spend some economic resources on being good to one another, regardless of anything else we might vote on".