Angold suggests Monomachos was trying to get the state back onto a peacetime footing after years of war under Basil, and trying to account for economic diversification and the demands of a shrinking tax base. I think that seems reasonable, though I've not seen any other serious suggestions for Monomachos' behaviour besides the overly simplistic "he wanted to spend it all on buildingzzzzz".
Yeah, I'm familiar with Angold's argument. But I disagree pretty strongly with his characterization of Basileios' foreign policy - which is supposed to have destroyed all of the Byzantine buffer states and allowed invaders from the east and north to threaten Byzantine security. That's ridiculous on the face of it - per Holmes, Basileios
created a belt of loyal buffer states in the East, and a rump Bulgaria in the northwest that had to be destroyed after it proved to be insufficiently loyal. Shit, he even gave some of those loyal Muslim vassals military governorship over Byzantine territory to help get them the resources they needed to ward off threats from various Buwayhid warlords. It was his successors who, searching for easy victories to shore up their legitimacy (for as husbands of Zoe they were not actual dynastic monarchs, and needed independent claims on the throne), despoiled the eastern buffers and ruined Byzantine security. Argyros and Monomachos were most egregiously guilty of this (in Syria and Armenia respectively).
The financial motivation is fairly reasonable, and I suppose you can't totally fault Monomachos for
trying reforms of various kinds, except that they all seem to have been dismal failures. He seems to have taken security for granted, and since security was basically the primary function of a premodern state, such a viewpoint was inexcusable.
That might not be an entirely unreasonable suggestion though - what did Roman emperors spend money on besides war? Building stuff.
It does seem that there's a certain extent to which Basil's successors are expected by some historians (and presumably contemporaries) to be like Basil the Super-Emperor as if Basil's policies were awesome by definition.
But I'm not altogether convinced that the interpretation that Constantine IX and such were not fit to rule is all wrong, either.
I agree; nobody could live up to the mythologization of Basileios' policies - not even Basileios II himself.