The reason is simple … distance.
Theoretically, SketchUp’s model space extends to infinity.
In practice, SketchUp is capable of models several kilometers in size.
Thus urban planners can use SketchUp to create very large models encompassing many city blocks.
While others can use the same SketchUp tools to model much smaller objects, say, a faucet handle.
SketchUp’s camera behavior supports both.
As you zoom by rolling the mouse wheel the Camera travels straight towards or away from the exact point in 3D space upon which you have placed the cursor.
The distance the camera travels with each revolution of the scroll wheel is proportional to the distance between Camera and cursor location in 3D space.
The greater the distance between Camera and cursor location in 3D space …
The greater distance the camera travels with each revolution of the wheel.
That proportional behavior enables the camera to traverse great distances efficiently while providing increasingly precise control as the distance from camera to target becomes less and less.
Consequently when you back the camera through a face the distance from camera to target (face) is minimal and camera travel per revolution of the scroll wheel is, as you now know, in proportion to that tiny distance.
It’s best to stop the moment you’re lost inside geometry or inadvertently zoomed into outer space.
New users tend to continue flailing about zooming, orbiting and panning which readily purges the desired view from the camera buffer.