It doesn’t download these by default. All the wallpaper and screensaver downloads are user initiated in their respective UI. Did you click the download button on them by any chance, and forget about it?
If I clicked download on some screensavers, I would never think it had downloaded _4K@240FPS resulting in 47 GB of lost disk space!_ The fact that a big warning doesn't come up with this fact makes it even less excusable. It's like if I went to the dentist for a filling and received a bill for 1k because "you know, those titanium fillings are expensive". Who asked you for titanium you lunatic?!
You're conflating a "one way door" with a "two way door" here. The permanant loss of money is a one way door you can't undo. Opting into a screensaver is a two way door you are a few clicks from undoing.