>I guess Im questioning why Waymo doesn’t just IPO, or raise 100% private raise by Google.

Why not 100% internal funding, not sure, but the reason why companies don't always IPO is because taking on debt is more efficient (i.e. it's cheaper in terms of cost of capital) than equity, because of the "tax shield" effect, debt can be raised in a non dilutive manner, and a few other (less important) game-theoretic reasons.