ISTR pg has an essay on this somewhere, but anything you do to make the top-end payout for a business starter worse has a disproportionate effect on their willingness to incur the risks of starting a business. If SarbOx makes it harder to take a company public, which is one way to get a payout, it can have that effect. Economics isn't just about first-order effects.

In fact, it is sufficient for it to be perceived that it limits your top-end gain, even if it doesn't, and I think that I confidently say that such a perception exists in many people's minds, even though I could not say a word about SarbOx's true effects.