[jonknee]

When you buy a share of SPY you're not paying that cash to all the S&P 500 companies, you're paying it to another party that already has a share of SPY. IPOs give money to companies, but trading shares between parties does nothing for the company and contributes $0 to wages, equipment, R&D, etc.

I own shares of SPY, if I sell them to you what exactly changes?

[refurb]

Yes, the cash doesn't go directly from you to the company, but you're creating a market by which a company can raise funds through a stock offering.

Take away the market and the company wouldn't get any money.