For asset managers, the reason you form a SPAC is because you will get upside in the form of convertible warrants that will net you ~20% ownership, essentially for free (cost of your time to find and close a deal, and minimal upfront cost), assuming the stock price outperforms the original issue price.

You should ask yourself why an existing owner who believes in the future of their company would be willing to give up 20% upside to avoid the cost of an IPO. I would suggest that the very act of giving up this 20% promote for a 'hot' unicorn tells you something about the valuation that the SPAC eventually does a deal at.