This scrips runs but there is no reduction of files in the folder

expecting only the latest 5 files to remain in the folder

function getOldFileIDs() {
  // Old date is 21 days
  var oldDate = new Date().getTime() - 3600*1000*24*21;
  var cutOffDate = new Date(oldDate).toISOString();

  // Get folderID using the URL on google drive
  var folder = DriveApp.getFolderById('1YS60U0CtsY4V*****Lqxb6-_TS0LMho1');
  var files = folder.searchFiles('modifiedDate < "' + cutOffDate + '"');

  var obj = [];
  while (files.hasNext()) {
    var file = files.next();
    obj.push({id: file.getId(), date: file.getDateCreated()});
  }
  obj.sort(function(x, y) {return x.date < y.date ? 1 : -5});
  obj.shift();
  var fileIDs = obj.map(function(e) {return e.id});
  return fileIDs;
};