@mcc Oh! Yeah. It's because they don't have a well-defined canonical composition order, unlike modern Jamo, which do.
A weird bit of trivia: there is no composition for hanzi/kanji/hanja/chữ Hán characters (what many call "Chinese characters"). You can't just build one in Unicode. If you could, they'd also be in this list, for the same reason that Old Hangul Jamo are disallowed (which were only added because scholars needed them).
@alilly@mcc@xgranade yeah, i guess the difference with the hangul thing is that it's a safe assumption no one is using thsoe characters to write their names in modern times, which is not the case for greek or cyrillic -F
@mcc@Hearth@xgranade Yeah but that's much harder to do anything about, unless you want to ban modern speakers of languages written using Cyrillic from using names in their native language, which… don't do that.
@sysop408 @evan As an information architect I constantly warn clients about the "Aardvark effect" where users will just default to the first item e.g. in a list of tags for content publishing. Counter this with the wine list effect, where everyone picks the second-to-most cheap wine to the point that restaurants list the one they want to offload there.