inter-library loans beg to disagree.
The DDS codes subject to shelf location. For a given library, materials selection is largely relevant to its own interests, and in many cases, location and local culture have a strong influence over that.
(As I've discussed in an earlier comment, DDS is not the only shelving system used, though it's a commonly encountered one in the US, and serves as a basis for numerous others. There are also non-subject based shelving systems, though those are typically not publically-accessed.)
What part of that sentence is not contradicted by inter-library loans? The books come off the shelves, and must be found there. They serve a wide geographic area, sometimes even the whole world (my mother was a librarian at several very specialized libraries and they participated in both receiving and giving loans involving other libraries around the world. It is true that the physical shelves in a library in (say) Germany will not be organized using DDS, but it remains true that the physical shelves can serve a wide geographic area.
And this is not even to comment on those specialized libraries that people will travel from around the world to visit. Same physical shelves, world-wide service area. These can include libraries focused on individuals (famous historical figures, for example), or academic libraries with particularly rich holdings in certain areas, or libraries that just happen to have the only instance of a set of books/documents.
The fact that DDC was developed at an academic library (Amherst College Library) doesn't refute this --- origin stories are not present-use stories, and Amherst have largely converted to the LCCS (see: https://www.amherst.edu/library/find/finditfrost/call-number... https://www.amherst.edu/library/find/finditfrost#tab-44437).
The LCCS, though influenced by DCC, is distinct. It still reflects a US-centrism, though with different emphasis. History of the Americas occupies two of the twenty alphabetic major classifications, and each of political science, law, education, agriculture, technology, military, and (separately) navel science, has its own major classification, reflecting the interests of a government ... and that government's library shelving concerns.
Specialised libraries rarely use DCC in my experience. Medical libraries often use their own specific classification, and academic libraries in the US as noted above typically use LCCS, though some retain DCC or their own ideosyncratic classifications (both are generally being phased out for LCCS).
For the University of California, an academic library with a strong inter-campus ILL programme, local circulaty exceeds ILL within the multicampus system by over an order of magnitude (1.6 million vs. 135k https://libraries.universityofcalifornia.edu/about/facts-and...). For a local public library with few exceptional holdings, ILL circulation is likely a far smaller fraction of circulation. (Some have regional lending arrangements with peer libraries, independent of ILL. This still remains a small fraction of total circulation.) Much use of materials is within the library itself, captured only (if at all) in reshelving statistics, though those are hard to find.
(I used the UC library system only because it's among the few that have available statistics.)
The point remains that the principle focus of a cataloguing system is for local use and management of a bibliographic collection. ILL happens to be an incidental and compatible use. It is not of itself a major factor in classification system development.
If you have any substantive argument to the contrary, I'd be happy to hear it. You've not yet made one.
> The physical shelves in a library only serve a single, small geographic area, not the whole world
which is the line I was responding too.
If you're a regional nonspecialist nonacademic library where that split is far more likely 99%/1%, which do you solve for?
I am telling you flatly that your assumption and premise is false. Libraries, in the overwhelming majority of institutions, serve local communities, in the overwhelming majority of transactions. I've provided data to back my argument. You ... continue to hand-wave.
If the labels are placed on the book at a similar location, then any book that is out of its proper would be significantly more obvious without having to resort to reading the label of every single book.
Of course the techie solution would be to barcode every book and then have a robot on each shelf that scans the barcodes after hours...