Because SketchUp was never designed to be a CAD clone (of AutoCAD, Revit, anything else,) and never will be. SketchUp has been called the “unCAD”.
Think of all the CAD clones over the years that have withered and died and are no longer here.
You group or component “fractions of the model”, and assign them to “use” some unique layer.
(Keep all primitives associated with “Layer0”.) Layers in SketchUp are visual masks, not geometric collections!
Then you can switch off other layers so that the “fraction” is isolated.
You can click it so it’s selected, and then from the context menu choose “Zoom Selection”.
(A shortcut can be assigned when something is selected, by going to Window > Preferences > Shortcuts, scrolling to “Edit/Item/Zoom Selection” and then assigning a new key combination in the “Add Shortcut” box.
If you think you’ll be needing to isolate this “fraction” often, then that is a good time to set up a custom non-animation scene page with this “fraction” isolated (only it’s layer and “Layer0” on, the camera positioned and zoomed to suit, whatever special visual style you need for this view.)
SketchUp scene pages are most similar to creating user named “model space” views in AutoCAD.
ADD: If you think you’ll be doing the same kinds of scenes in multiple models, then it may be time to create your own model template with standard scenes pre-set.