Comment by Timwi

I think we're getting at the heart of your misunderstanding. You seem to feel that we're running out of codepoints in Unicode (the “limited number of shelves” analogy). This could not be further from the truth. Although the number of codepoints is technically finite, it is extremely large (over a million) compared to how many we need (currently only 160,000 are defined, and for obvious reasons the rate of new additions is slowing down). The Unicode roadmaps main page[0] displays only 5 of the 17 available planes because the remaining 12 (each 65,536 codepoints large) have not yet had any characters assigned to them whatsoever.

[0] https://www.unicode.org/roadmaps/