Trump had some very damning information.

So DJT has known for over a year that they, NARA, wanted the documents that he took with him when he left office. He even gave them 15 boxes. So why did he keep anything at all?

There's only one explanation.

He had some damning information on someone with great power. He took it with him because felt like he needed the leverage. He stalled NARA for quite some time, but ultimately turned over 15 boxes. When the contents of the boxes were reviewed, whatever it was that they were looking for was not there, so they had to get into his residence. Thus the need for the warrant.

If the documents he had were damning to himself, he would have destroyed them long ago. No way he kept anything that would implicate him in anything nefarious. DJT has known since he took office that they were out to get him, and they would leave no stone unturned to destroy him. Nothing can convince me that he kept something that would hurt him. I just don't think he's that stupid.

What would compel DJT to keep any classified documents at all? For what does he need them?

The raid was a fishing expedition. He took something very valuable with him when he left Washington, and they were desperate to get it back. Nothing else makes sense.

It's even likely that DJT knew what they were looking for, and let the information leak just to see how far they would go to get it. He hasn't made an effort to get out in front of this because they didn't find what they were looking for. Even if they did, it will never be revealed because it was always detrimental to someone very powerful.