Cool!
Zero problems with Manjaro here.
For those that don't wanna go to reddit.
Nate's answer:
Because nobody implemented it yet. :)
wallpaper cannot span multiple screens
Most other DE's and even just regular WM's when used with feh can use a single large wallpaper spanning multiple screens, eg 5760x1080 for triple head. KDE 5 however can not do this and it also blocks feh from working as well. This used to work with KDE 3 and earlier but appears to have broken since then with the rewrite.
I wasn't sure which component was the better fit, Image Wallpaper or Multi-screen support so put it under Image Wallpaper since that is likely where it needs to be fixed.
Seems promising! Pretty cool indeed!
"opressive regime"
Thank you so much! The dev updated the theme (I am using Kripton https://github.com/EliverLara/Kripton)

Easy there dude. You are discovering yourself. It's OK. You're a beautiful being.
Hello!
Agreed