E.g. Ginko did $100m in rev in 2021 and is at a 20B market cap.
Why would a company do this? Simple: Money. Spac sponsors "guarantee" a ~20B market cap. Investment bankers in a regular IPO might offer $4-5B (still 50x sales).
So what's the difference? Spac sponsors are willing to take "venture" style risk, and traditional IPO underwriters are not.