You can't ignore the indirect influence. The same way people care about resale value of their car or house, the investors that purchase at an IPO know that index funds will buy their shares and can therefore make more and bolder investments.
Of course I can ignore the indirect influence; if the company had no actual value at IPO its share price would plummet. Also, by definition the S&P 500 only includes companies which have had 4 consecutive quarters of positive GAAP earnings, so the shares would have value on the public markets. Specifically, they'd have to have enough value to be among the 500-or-so largest positive-earnings companies by market capitalization. Hardly value that can be attributable to indirect influence of an index fund.
You're looking at it too statically, and ignoring the full ecosystem.
If I'm an investor that buys at IPO time, how many companies am I willing and able to invest in if I have to wait for the profits to come in through yearly dividends? And so, if I'm a VC, how many companies am I willing and able to invest in if the IPO market is much smaller? And so, if I'm an entrepreneur, how many companies can I found and create value from if I have very little chance of selling them off?
The index funds are the terrain that sustain the "wealth creators".
