Inserter won't take items out of space platform hub

[Computerizer]

I've sent some ammo up to my space platform. I have a long-handed inserter (filter set to the ammo) reaching into a cargo bay attached to the space platform hub. But no ammo is coming out. The inserter's status says "Waiting for source items." Why is it unable to pull from the space platform hub's inventory?

[mmmPI]

You can use inserter to take things away from the space platform hub.

You can't use inserter to take things away from the cargo bays.

[Ranec1]

It is very non-intuitive to be honest. I get why they did it that way though. This also means you to choose which direction to extend as you need access on a few sides.

There is a similar gotcha on the planetary bays where inverters cannot be used to "put" but can only "pull". I had a plan to use the hub as a temporary chest for starting but those hopes were quickly dashed.

[Ranec1]

The bays also allow more orbital drops in addition to capacity. So a few are handy early on to ship everything down you are collecting.