There's likely enough for more convictions, but two things:

1) Maxwell was under prosecution at the time, so some of it was related to that.

2) The kind of people being mentioned as potential indictees are the kind who can do something about it.

Co-conspirators are prosecuted in parallel or semi-parallel all the time, without waiting for the core prosecution to conclude.

There was no reason for why the administration had to wait for the files to be unsealed to go after anyone it wanted to. Unsealing them only makes the records available to the public at large, not the rest of the DOJ.