These two (and maybe others) used to be in Fedora repos. They also used to be in Debian’s an Ubuntu’s. To my surprise, they’re not anymore, whereas MariaDB, PostgreSQL, sqlite, etc. are.
I wonder, did something happen for the distros to stop shipping them? What triggered the drop of the packages from the official repos?
In most cases the packages are included if they have an active maintainer and dropped if there is no maintainer to package them for distribution.
I cannot speak to those individual packages specifically but if you really need them then you might volunteer to support and maintain them for fedora.
cassandra had no maintainer for more than 6 weeks. See https://src.fedoraproject.org/rpms/cassandra/c/8fcb780b616a034aa5d787d04d631ac1f815f694?branch=rawhide
If you need it and if you want to maintain it, maybe that would be a job for you.
Same for couchdb, see Tree - rpms/couchdb - src.fedoraproject.org
Clear! I’m not sure how can I become a maintainer, but I’ll check it out and see if I can be of any help.