This is a good thing imo. Letting any and all of the most mediocre candidates easily write customized cover letters will severely dilute the job selection process even more than it already is. It's the same reason you need to send out dozens of resumes on indeed to expect any sort of response. Indeed has made it easy, too easy, to get your resume out in front of companies and why most immediately go in the trash bin as soon as it reaches a hiring manager.