To be fair they wanted to keep everything representable with 16 bits and that wasn't going to happen without the Han-unification. The mess when everything still had to move to a 32 bit representation has been far reaching, many programming languages went from exposing code points atomically as "char" to some half encoded nonsense value that just happens to also be a valid standalone value in UTF-16 most of the time and a source of bugs when you least expect it.