A station isn't mobile like the Seed Vault is. Imagine, for a moment, the Emerald Chain, Train or whatever those Green Meatbags call themselves, finding the Seed Vault as an immobile station. The Orion's would attack and most likely capture the station. Now you have the Orion's with the power to destroy or create every single planet in the Federation in the palm of their hand. Having the seeds of every single planet in the Federation would allow the Orion's to enslave every single race in the Federation by being able to re-create the Federation member's planet on dead worlds to enslave them on.
A war breaks out between the Rebels and Orion's, the Orion's simply threaten to destroy the seeds of the Rebel's home world or the Orion's would simply destroy the seeds, thus erasing the home world of the Rebels forever. Such power is even more great then than what Discovery is holding in her memory banks.