Why are all homepage demos not displayed until I install the default demo?
Let us explain the theme import process first. So you can have an idea behind giving a default demo first, and availability of other demos once you install the default demo.
If you import default demo, then service demo, Or vice versa, it will mix up the pages/contents with each other, so we kept separate.
The reason to enable homepage demos after the default demo installed is, In the default demo, it imports all the contents like pages, posts, CMS pages, Inventory, etc. Once they are installed, we are providing other homepages to install for users. The other homepages(excluding default) demos will import only the homepages, not additional contents/pages/posts/inventory(since they are already installed in the default demo). The purpose behind this is to speed up the imports of Homepage demos and make the import process smooth, and work with lower server configurations.