Yeah, but every app would 'just work' if we have a level of indirection with an IME by default, even for languages with Latin characters.
I mean, there is a reason why Windows & macOS all selects a similar architecture on text inputting.
Yes, there is a reason. Microsoft and Apple want to make money in CJK countries. And they have architects that make system-wide decisions.
That is not how Linux works. Companies contribute where their business is. That is server or embedded. After Canonical closed bug number 1 https://bugs.launchpad.net/ubuntu/+bug/1 no big player is interested on Linux on the desktop anymore. Individual contribute what they are interested in and what they know best. I fear most Westerners don't understand the challenges of CJK and other more "complicated" scripts. I myself "blame" Americans if they do it wrong and something accepts only 7 bit ASCII. I can fully understand if CJK or right to left people blame us "8 bit people" (character set, not coding) for doing it wrong. We just don't get it, that's a fact. But I don't think studying Korean etc. is a realistic solution. The only way to change it is to have more people and companies contribute that a) need it and b) really understand the user needs.