If there are current legitimate legal risks to issuing all their publicly-sellable equity via an ICO? Why not do only some of it as crypto coins?
What's stopping them from issuing a few coins even now? They don't need to need the money. They need to prove that ICOs can work. They are the best placed company in the world to do this: are at the intersection between tradfi and defi, and exist in a country where regulations do exist and do get enforced.
Just because Coinbase operates within the crypto space doesn’t mean they must themselves embrace and utilize every mechanism within the space. Even if they believe in ICOs specifically, they may have not made sense for their specific business (see other comments about regulation)