Kind of amazing too that it was personally created by King Sejong himself. Even today there aren't many people who can do such thing, let alone a monarch whose handd would have been filled by other duties.

There are ... speculations that King Sejong was not fully independent in the creation of Hangeul. He may have delegated parts of the task to courtly scholars. (But all the evidence either way has been lost to history, and so speculation it remains.) There are a few "historical" dramas which make this their premise.

Admittedly most of my impressions are from watching K-dramas but I get the impression that the monarch is somewhat superfluous in bureaucracy-heavy systems like in Joseon and China — and that the government was generally happiest when the kings did nothing. All they have is free time and education.

Plus you should look at Hangul as a political action. Educating the commoners creates a bourgeoisie class that can be the king’s allies against the noble and bureaucratic classes. People who can read laws and write complaints are less subject to the whims of corrupt local officials.