Why would a knife be a problem in a checked bag, even if it hadn't been sealed in the original package?

I've asked TSA people similar questions when they checked my bag. He said that the item was blocking view of what was underneath it.

I'd guess it's not the packaging, but a big piece of steel blocking the xray view.

The x-ray machine aren't 360?

If 360, I wonder does the operator perhaps not trust it?

probably different fidelity of scanner, I'd guess. This was in 2018-2019