They make hardware prototypes. When you do that having your own machine shop can lower the iteration time and thus speed up the development.

Just from the top of my head: waymo develops their own lidars, akamai obviously needed a ton of machining for the kite, project loon probably had machined components. And those are just the flashy examples we heard about outside of the company. They can have ton of other projects which didn’t get to the point where we heard about them but required hardware prototyping.