Why can't I use the paint bucket on a component or group?

If you paint the container you can change the material to a different one without opening the container. That’s not the best way to apply materials but it can be done.

You can replace the materials on the faces by painting the default material on them. in the Materials window there’s a “dive flag” icon with the default front and back face colors. Use that to repaint the faces. Or delete the applied material from the In Model library and it’ll get replaced with the default color.

There’s not much point in learning how to change the orientation of materials if you only plan to paint the containers since you won’t have that option. If you paint the faces, however, you can right click on a face and choose Texture>Position and control orientation from there.

Another benefit of applying the material to faces instead of wrappers is that you can apply different materials to different faces so you can apply an edge material and a surface material and make it look like plywood.

I couldn’t have shown the edge grain of the plywood or indicated end grain on the hardwood pieces by painting the containers.

And it really doesn’t take long to do it.

Also, if you use decent texture images of wood, you can pick out different parts so the material doesn’t appear to repeat. The seats for these stools are made from two pieces of wood glued together although I drew them as a single component. By painting the surfaces, I was able to pick out different parts of the board for each half of the seat. Not an option if you paint the container instead.
Perriand Stools