So Jottacloud does not provide any file transfer, and due to this forum post they do not provide an official API for developers. I don’t see how external programs then should provide an “official” direct connection with jottacloud. Obviously jottacloud does not want that. Programm developers are in this respect quite a bit dependent on the providers.
Further more, Cryptomator for desktop is designed to work with the providers sync client to allow users of nearly all storage providers (as nearly all have their own sync client) to store their files privacy protected online .
If you want to access you cryptomator vault directly with a desktop app, third party apps will fit better for you (but of course they will also need to have an api/webdav or other connections provided by cloud service).
Keep in mind that the cryptomator mobile apps connect directly to the cloud service. You will not be able to connect to your cryptomator vault with the mobile apps, if the vault is on jottacloud.