Howdy!
The planets in the Demo build rotate for the sake of variety and so that Demo players with various kinks can enjoy content that would otherwise be pay-walled. It's a bit of a "Damned if you do, damned if you don't" situation, however. For every player that just wants access to one kind of content, there's someone that wants access to something else. The most I can advise is that content will regularly revolve back into the Public build, and if you'd like to have access to all planets at once, it may be worthwhile supporting the project.
In terms of filtering scenes by kinks, I 100% agree. A better content-filter is definitely on my to-do list, and I'm fiddling with initial builds of it at the moment. Thank you for your suggestions!