It's not like we don't know how to do this stuff, we just don't invest enough in it.
Another USA company tried to do that as well. They called their OS "Windows Phone" and it withered and died because a fractured support for software people care about doesn't make a useful device.
A Chinese company tried to do that as well. They now again ship Google Services next to their own Huawei services in Europe because without software support, their smart devices weren't useful to users either.
There are also plenty of other mobile phone OS, that are not compatible with every phone and that is the main issue why they are not widespread. Phone that I own is supported not only by Android(and Android forks), but also couple of other mobile phone OS. The trend is that in future there will be more choices for OS, that might satisfy those users, that are currently not happy about Android, but have no other choices at the moment.
There are at least 10 other mobile OS choices - most of them are based on Linux, but current share of those is ~0,1% out of ~6 billion of phones. In total numbers that is only 6 million devices. 6 million device market is a significant number for any company, not to mention, that this number is only playground compared to 1000x larger world market of mobile phones.
Therefore, logically, Apple should be the one paying app developers 30% of their revenue. Witout them iPhone would be an overpriced paperweight.
South Korea is a small market. The US company is famous for mismanaging its mobile operating systems for more than 2 decades.
The Chinese company didn't "try" to do that, it was forced to. But guess what, in China, where most external apps are banned, there's an entire, completely separate ecosystem.
You do need a combination of skill and critical mass. I don't expect South Korea to achieve this, but for example if there's a bigger alliance of say, South Korea, the EU, etc., where they put resources into encouraging an OS based on open standards, that starts to look feasible.
App developers will need support, but they can port their apps. Especially since this OS doesn't need to start from scratch, it can be based on AOSP.
That's probably the biggest thing Google/Apple are afraid of this point, that a fully open/interoperable mobile OS is somehow enforced. They either have to open up their OSes to be in key markets or they're forced to let someone else create that OS.
iPhone has branded itself as status symbol that people are rich and can pay and maintain lifestyle that includes ipHone - Androids, well - it is replacable and will be eventually.
So you are saying Google / Apple are above the law, capitalism is more important than democracy?
Where does this end? They might as well start acting as mafia, resort to raketeering and break you legs if you don't show up for work.
Is there any other reason i missed?