For the very same reason that Eve saw that the forbidden fruit was good for food and that it was a delight to the eyes, and that the tree was to be desired to make one wise. She liked it. There is lust of the flesh because it feels good even if it is wrong. Same with lust of the eyes, it is pleasurable even if it is wrong. Same with pride of life.
We sin because we like it, it gives us pleasure, it makes us feel good, it's fun.
Maybe what you are confused about is why any of those things are wrong. That is a different question.
Why did Eve see that the forbidden fruit was good for food and a delight to the eyes, and to be desired to make on wise?
Why did she like it?
Why is there lust of the flesh because it feels good even if it is wrong?
Why the same with lust of the eyes?
Why the same with the pride of life? WHO set up these principles by which all this is true? WHO determines who will and who will not?
"Maybe what you are confused about" is because you can't even comprehend my question; you still fail to see what I'm getting at, that your worldview refuses to see. But, we can do this till you get to the end of reasoning, to see that whatever comes to pass, does so by God's decree, which is not at all confusing. I'm not sure that even then, or no matter how many times I repeat this, that you are even able to see the point. It just doesn't appear in your self-deterministic mindset.
So far, I'd like to believe you only purposely turn your back on my obvious question, of why some choose evil and some choose good, yet never anywhere near 50-50, but according to God's election and causation. You wiggle but don't even seem to know you are doing so. You haven't begun to show what the difference is, between what happens in the two cases. WHY do the few become saved, but the many consigned to reprobation? Why not approximately the same? WHAT makes that difference?
But if you are really puzzled as to what I'm asking, and all you can do to explain is to kick the can of causation on down the road, we can do that.
Continue.