I don't know, at this point, it just feels personal, specifically against Dwight, right?
I don't exactly blame you for not remembering, it being so long since the last update, but it has already been said that what is opposing MC isn't the will of the world, the Spirit King they met earlier said it was something else that was "unreasonable and illogical"
Maybe whatever it is, it goes against Dwight because he's "out of sequence". As in, he's not a Demon Lord who got empowered, went against mankind to be rekt by the season's Hero. He's just a "regular" mofo who calls himself Demon Lord and has the power and intelligence to back it up, no "Will of the World" involved or whatever it is.
Or more simply, Dwight broke the planned scenario and whatever created that scenario in the first place doesn't like it so it keeps empowering "JRPG-like staple characters" to defeat him: a Hero, a Saintess, an Isekaid'd earthling... And now it's the Demon Lord, another one of those. This is just my personal theory, though.