Following funkathustra’s three points, I need to add another:
Many vendors will have STEP files available for download or by request (I have yet to encounter one that didn’t provide me a STEP file for the component I was interested in.) I use FreeCAD to open that Step file and export a mesh. From there I open the mesh in MeshLab and export it as a COLLADA .dae file which I can then import into SketchUp. I’ll save that file out into my SketchUp parts library so the next time I use it in EagleCAD and export it through EagleUp, it will pick up that component. Yes it’s a process to get that component in SketchUp format but it sure beats having to draw it from scratch.