Hi Nodeity, welcome aboard!
Coollector Movie Database is a movie database like the IMDb, or TMDB, etc... When you go to the IMDb, you don't ask them to remove the preloaded stuff

Our movie database is the foundation from which you'll rate what you've seen or mark what you own. Then you'll use filters to display only what you've seen, or only what you own (or whatever you want to display).
It's very common to want to display only what you own, that's why there's a dedicated shortcut to quickly make a filtered search that displays only the movies/series that you own. You click the "owned" shortcut, it's only 1 click, and you see only your stuff. If you want to display what you own all the time, you won't even have to click the "owned" shortcut again because when you'll close the app and re-open it, the app will remember that you were displaying your owned stuff.
There are several filter shortcuts: "movies" (resets all the filters to display all the movies), "rated", "predicted", "owned", "playable", "wished", etc...
Hopefully you'll end up appreciating that this app can do more than cataloguing your stuff. You can rate movies that you've seen but don't own, the directors/actors have their complete filmographies, you can discover great movies you had never heard of, the IMDb ratings and the predicted ratings help you decide what to watch, etc...