It's due to long history of living in a....twisted? faith.
In fact the country was one where the church, or the worshipping of the Gods, are the core of the governance.
Where the sovereign is chosen among those who have passed the trials from the Gods and was basically also the Pope, ruling from the first temple.
Because this country was actually created by a God anchoring himself to the land and use magic to turn it from the barren desert it was into the habitable country it is now.
Nobles' most important duty in the Gods' eyes are to expand their population and to fill the 'core' of their area (or in case of the sovereign, the country's) with mana to keep it from reverting into the barren land it was (like when monsters consume the magic)
Then a long time a go, a queen want her son to inherit the position however her son didn't have the qualification.
So instead she made a magic tool that can replicate the functions required to run the country_core.exe and give it to said son.
Said son, not knowing any better, pass it on.
Over time the tradition of taking trials of the Gods for that magic tool was forgotten, and more things changed.
And then recently the country lost that magic tool in the coup (along with a lot of dead nobles) and is slowly declining because while they can try to maintain the mana supply, they can't operate country_core.exe and are having problems because of it.
When Myne eventually go to school, which IS also the same location as where the first church was established....well, Myne being Myne she ends up entangled in things.