There are only a few spaces for migration options/paths which need to be manually created.

In order to migrate a question when there is no migration path, flag for mod attention saying that it should be migrated. If it's not obvious why, an explanation can be helpful, although we can ask mods from the site to be migrated to if it's on topic on that site.

In order to create a migration path, migrations to that site should be required frequently.

Quite simply, as we're a small site, we have neither the number of incoming or outgoing migrations to have any migration paths to or from here yet.

There are only a few spaces for migration options/paths which need to be manually created.

In order to migrate a question when there is no migration path, flag for mod attention saying that it should be migrated. If it's not obvious why, an explanation can be helpful, although we can ask mods from the site to be migrated to if it's on topic on that site.

In order to create a migration path, migrations to that site should be required frequently. The only exception to this is the meta of the site the question was posted on.

Quite simply, as we're a small site, we have neither the number of incoming or outgoing migrations to have any migration paths to or from here yet.

In other words: yes, it's possible to add more migration paths but we need to actually perform a number of migrations to the site we want to add a path to first

For more information on this, see 'Migrate to any site?', including this answer on why we can't just list an arbitrary number of sites.