Great, Unicode is already a fragmented mess, and now the standards organization justifies its existence by adding characters that do not exist.
An earlier poster asked why anyone thinks Unicode is fragmented. The answer in one word: fonts. Different fonts support different subsets of Unicode, because the whole thing is just too big. If you expect your font to mostly be used in Europe, you are unlikely to bother with Asian characters. if you have an Asian font, it probably has only English characters, not the rest of Europe. huge. If you have a font with complete mathematical symbols, it will include the Greek alphabet, but actual language support is a crapshoot.
You are correct in the reason that most fonts only contain a subset of Unicode code points. There are thousands of code points. Most documents will only use a small subset. Why should I have to have all those Chinese or Arabic characters when I only write in English, Spanish, Portuguese, and Hawaiian? People who read and write Hawaiian have fonts which support the Hawaiian letters `okina and kahako. Chinese have fonts which support the Chinese glyphs.
As for language support, that isn't a font's problem. It's up to the writer to know how to intelligently combine glyphs into words, and words into coherent thoughts.