It must have been much less of issue when UTF-8 specs were formalized in early 90s, as memory was expensive, and electronic communications between CJK cultures were minimal; computers just had to have the correct font for a single specific language, and others didn't even need to render, let alone correctly. Being able to display similar letters outside of a specific language must have been a bonus.
Today it's a much pronounced annoyance as software is globally distributed, but until the Unicode Consortium figures out how to normalize this CJK situation, the font switching hack has to go on and there just can't be a single font that could render everything.