The point about the layers (tags in SU2020) is that you need to keep Layer 0 assigned to all raw geometry. You only assign other layers to objects (groups, components, and text/dimension entities). Layers/Tags in SketchUp are not layers in the same sense as in 2D application and in SketchUp you do not put things on layers. A layer is just a tag you assign so that you can control the visibility of the objects in the model space. You can have layers for the wall group and floor group as well as for the Lalley columns and other objects in the model. Then for example, if the walls are in the way you can turn off the Walls layer to open up the view so you can work in the basement more easily.
Maybe the thing to do is just accept that Layer 0 should always be active and all edges and faces should keep the Layer 0 tag. It’s kind of like what my father told me when I was starting my sophomore year in high school and was getting ready to take Physics. He advised me to accept that certain basic facts had been proven enough times over the years that I shouldn’t worry about them. Like Force equals Mass time Acceleration. It just is and the sooner you accept it, the easier your life will be. 
