What is it about us that we all sin, yet the angels did not all sin?

I was reading Romans 11, and 11:32a says: For God hath concluded them all in unbelief ‬ ‭KJV‬‬ I didn't understand that phrase, concluded all in unbelief, so I read a number of commentaries, of which I found Adam Clarke's the most helpful. But after reading through all the notes I took,the mystery remained to me is that we all sin. Why? The angels didn't all sin. I know God knew what would happen when he created Adam. He must have had a reason, or reasons, to create him in such a way, that he 1) was capable of sinning; 2) was the progenitor of the whole human race (as opposed to angels, who were created all at once); and 3) his proclivity to sin would be passed down. After I posed this question, and received answers that were helpful, I thought of this: We all sin, every one of us, because we lack something. God originally created us in His image (Gen 1:26). Yet as Christians, we need to be sanctified, which means we need to be changed into His image, and it won't be completed until we see Him. So we lost something of that image in the fall. Angels are completely different than us, and I don't believe we know enough about them to know why. At least I don't. There are theories proposed in answers and comments under this question Why can't there be another fall? that seem very plausible. I am hoping others can shed some more light from Scripture. Please not from a reformed perspective, I am neither a Calvinist nor an Arminian.