Why is there a index.php in my routing?

Hi all,
I am new to CI for like half a year and working on my second project using it. I wonder about one thing:
My "normal" routing works well, domain.tld/page1 etc, Apache is set up to drop the index.php
But when I use something like

PHP Code:

return redirect()->route('page1') 


the redirects are always going to index.php/page1
Why is that (and how to prevent it)?