imported photos showing up in imports but not photos

I'm using Photos 5.0 (161.0.120) on a MacBook Pro with Catalina 10.15.6

I just imported some jpeg files from a USB drive. They are showing up in the Photos app side-bar under

Library --> Imports

but they're not showing up in the side-bar under

Library --> Photos

Is there any way I can get them to appear in

Library --> Photos with all my other photos?

Just out of curiosity, why don't imported photos just go to Library --> Photos automatically? What's the advantage Apple perceived in designing the Photos app this way?