The affidavit doesn't include all the information the DOJ has, or information about whether Trump has committed a crime, it just contains information about why the DOJ thought the documents they asked for in the warrant were at Mar-a-Lago.
This is a civil matter and there is no criminal investigation because there is no evidence a crime has been committed. The National Archive stated that some important documents were missing and the Democrats immediately said Trump took them without any proof to support that claim; nonetheless, back in June the FBI without a warrant, inspected the area where the documents Trump took with him were being stored, and made suggestions for more security, which have been since implemented, and Trump allowed them to take whatever documents they claimed were relevant.
Now Garland asked for a warrant to search under Trump's bed and in his underwear drawer to try to find top secret documents Garland claims Trump may have secreted away there, and this is such an extraordinary request that the people have a right to know why they thought these documents were in his living quarters or if the search was just more evidence of Biden using instruments of government for political purpose as we get closer to the November elections. In Russia, Putin uses the instruments of government, the police and the courts, to attack his political opponents and the people have a right to know if that is what Biden is doing as a part of the preparation for the November elections.