SOX exists because investors were tired of being defrauded by the people running the companies. While SOX might make it more onerous to go for an IPO, it's still a good thing for public markets.
I suspect the real reason companies stay private for so much longer is not because SOX-compliance is too expensive, but because companies can take advantage of private investors in ways that they cannot get away with in public markets.
SOX exists because investors were tired of being defrauded by the people running the companies. While SOX might make it more onerous to go for an IPO, it's still a good thing for public markets.
I suspect the real reason companies stay private for so much longer is not because SOX-compliance is too expensive, but because companies can take advantage of private investors in ways that they cannot get away with in public markets.