If I had to sum up the reason in one word, it would be laziness.
Wild to read this from a modern perspective. It's like reading about women being shamed for being 'hysterical', or religious peasants blaming their natural sexual feelings on demons. It just doesn't hold up to scrutiny...
What is 'laziness' when applied to something that you clearly want to do? How can someone want something, yet simultaneously choose to not want it? Turns out the answer is simple, and the nerds have known it since 1801[1]: you don't exist. Your continuous, unified self is an illusion brought about for instrumental reasons.
Treat yourself like a system to be optimized, not an ineffable soul to be brought away from vice through logic. If you were tasked with improving a malfunctioning software system, you'd be laughed out of the room for starting with "well, clearly, the system is just sinful, and choosing to make mistakes."
[1]: Immanuel Kant, The Critique of Pure Reason, Chapter I.2.II.1: "Of the Paralogisms of Pure Reason"
Now to these conceptions relate four paralogisms of a transcendental psychology, which is falsely held to be a science of pure reason, touching the nature of our thinking being. We can, however, lay at the foundation of this science nothing but the simple and in itself perfectly contentless representation “i” which cannot even be called a conception, but merely a consciousness which accompanies all conceptions. By this “I,” or “He,” or “It,” who or which thinks, nothing more is represented than a transcendental subject of thought = x, which is cognized only by means of the thoughts that are its predicates, and of which, apart from these, we cannot form the least conception. Hence in a perpetual circle, inasmuch as we must always employ it, in order to frame any judgement respecting it. And this inconvenience we find it impossible to rid ourselves of, because consciousness in itself is not so much a representation distinguishing a particular object, as a form of representation in general, in so far as it may be termed cognition; for in and by cognition alone do I think anything.
https://www.gutenberg.org/files/4280/4280-h/4280-h.htm#chap7...For the more empirically minded that are understandably resistant to such an unnatural conception, try to find discussions of "laziness" in these articles. I'd be surprised:
https://www.webmd.com/add-adhd/executive-function
https://my.clevelandclinic.org/health/symptoms/23224-executi...
https://en.wikipedia.org/wiki/Executive_dysfunction