Waymo then installs it's fancy software on these boxes and uses it's Google connection (Maps, Waze, etc) to put people in those boxes and charge them a hefty profit, at least for a few years while it's the only provider. Waymo wants to be in control and collecting profits, while manufacturers subsist on small margins.
Obviously, this isn't a good situation to be in for Honda etc
If you're just hailing a ride, you care a lot less about the brand of car and it's amenities. You care more about the overall ride share service, price, etc. Very little of which Honda would have any effect on if they don't have some skin in the self-driving tech.
I do see a future in very high end & privately owned cars, which will quite possibly generate even higher margins for some manufacturers. Plus there will be a whole new world of innovative design opportunities in the self driving cars realm, in which the self driving part might end up being be the boring and somewhat commodity part.
From Waymo's perspective, that's exactly the scenario they want. Focus all your resources on developing a tech advantage that others can't match, and have others in the ecosystem serve the lower-margin stuff.
If this sounds familiar, recall Google Search and Web Content.
Examples:
-- Wintel --> Microsoft + Intel financially did much better financially than the legions of PC makers who designed, built, and sold products using the Wintel foundation
-- Android --> Similar, with Google reaping the profits.