Why does the library file weigh so much?

Question

Apple Final Cut

I edited a couple of short videos of three minutes each (usual screen recording of three minutes at 1440 by 720 and music from above). With the initial weight of the entire recorded video 200-300MB, the size of the library was blown up to 17 GB. Why? And most importantly, how to reduce it all?

The settings are set like this (someone with a similar problem somehow had the checkboxes set wrong, but I have everything right, sort of like)