All manufactured components have tolerances. Binning is used to minimize the impact of those tolerances on product quality.
Speaking here of high-end photographic lenses, not the junk you buy from some mass retailers who could care less about quality.
Any manufacturer of precision equipment uses binning to select which specific parts will work best with which other parts.
One common measurement for a lens cell might be the distance from the mounting face to a principle plane.
Depending on the quality of the particular lens, these might be graded as nominal, +0.1mm, -0.1mm, etc.
Other major groups of the lens are similarly binned.
So a front cell that's +0.1mm would be assembled with a barrel that's -0.1mm to achieve the correct overall dimensions.
This is universal practice in precision assembly.
The net result is that any particular sample of the product that you pick up would already have the selection made,
so you could likely dis-assemble and re-assemble it without seriously disturbing its performance.
Now, can you provide some published substantiation for your assertion that manufacturers lack proper measuring equipment?
If not, you're just blowing smoke.