On the detached database files, the file permissions change when detaching. i.e., The AD account (your AD account) performing the detach operation becomes the owner and the only person with permissions to the file. It does not inherit the permissions from the folder. Oddly, if you just detach and reattach, it would attach fine even though SQL Server Service account does not have any explicit permissions on the files. However, others cannot attach a file that you detached even if they are on the Administrators group until they are explicitly granted permissions on the files themselves. This is well explained in this MSSQLTips article. Quoting the article, if you want to retain file permissions on detach, set the trace flag 1802.
“SQL Server 2005 introduced trace flag 1802 which retains the database files permission after the detach operation. The trace flag is tested and still applicable with SQL Server 2016.”
Click through for several tips of similar ilk.