The danger of an IPO (from the perspective of the company going public) is the “IPO Pop”: you offer your stock at $20, by the end of the first day it’s trading at $40, and you realize you left a bunch of money on the table.
This is a benefit to the initial investors, who make a big profit day 1.
The inverse risk is the opposite (see Lyft, Slack IPOs): you offer your stock at $20 and it ends the day trading at $10. This sounds bad for you, the company, but it’s kind of fine — you raised the money you wanted to raise. In the short term, it’s bad for your investors, who just lost a big chunk of change.
My numbers here are made up, but the important thing is the spread: an IPO could pop 5% on first day, or 100%, or -80%. The difference there is volatility, which is what you have to pay a bank for — the risk that they lose money instead of popping.
In times of increased volatility (hello 2020!), you’re gonna have to pay a lot. The bank is going to underprice your stock to try and get a bigger “pop”, which, remember, means you’re probably leaving some money on the table.
A SPAC offers a compromise. “Negotiate with us instead, and avoid the pop (or the drop) entirely!” You reduce volatility in exchange for taking a private deal and potentially leaving some money on the table. It’s trading a bigger payday for a smaller risk, which looks pretty good right now. But in times of more financial normalcy, expect more IPOs.
My understanding of SPACs vs. IPOs is based entirely on Matt Levine’s excellent Money Stuff column, btw — go check that out if you want to read stuff from someone who actually knows this stuff.