> It's a non-selective herbicide in this context, it kills everything.

It is a non-selective herbicide, but it's not a systemic herbicide. It functions by interfering with photosynthesis, but since it is minimally absorbed via root systems, it must be applied directly to the foilage. You can spray it on the ground around a plant and that plant will happily ignore it. This is why the instructions are explicit about applying directly to the foilage during sunny days when the wind is light.

As a homeowner, I loved glyphosate. It was cheap, simple, effective, and could be applied in a selective manner. It's not the best choice for getting rid of broadleaf weeds in a lawn, but I used it all the time in my gardens to kill weeds and keep the bermudagrasses out.