Brand, inventory, names and addresses of all of the previous buyers, servers for the lock/unlock facility and possibly more than that.
I think it is genius, the bikes are expensive to buy, but $100 a month lease including maintenance is very popular among Big tech (especially if your company pays for it).
https://support.vanmoof.com/en/support/solutions/articles/44...
They could very well be losing substantial money on that. Leases only work if the quality of what you lease is high enough that you won't be bleeding to death on the availability guarantee. Financial lease insulates the lease provider from that but if it is operational lease then whoever inherits the leases might be in for a very hard time.