Overlord

[KrayZ33]

Dude. 1 guy can't controll everything at the same time. It's simply overwhelming.

If you kill nobles, some dudes have to replace these nobles, there are assets that's have to be distributed, you have to keep the populace somewhat happy so they don't become unproductive.

What does he even gain from conquering the world if he can't use the population properly? Why not seclude himself back into his Tomb?

The world isn't some 5x5km² field. He still doesn't know how many GM-Artifacts are around, or even players, he lost 1 of his lvl 100 companions already and had to revive her and he can't revive her again and again because it cost Yggdrasil money, but the money in this world isn't yggdrasil money as far as we can tell from the first 2 episodes.

He'll probably be able to control the Kingdom soon and won't have to deal with sheming unloyal nobles.
If you put just any noble onto the throne that doesn't have any legitimacy, you'll have another one who want's to be Ainz favorite and they scheme against each other.
So he'll make it look like the noble sucks and needs to be replaced -> Ainz will have to look into it and adjust the situation.