The ATS is the boogeyman of the resume writer. Having an ATS-friendly resume, with all the industry keywords from current job ads doesn’t guarantee that your resume will pass that ATS for the role.
There are a lot of different ATS software options, each with their own algorithms and scoring methods. Candidates can be rejected for not having the exact terminology used in the job ad, “collaboration” instead of “collaborative,” for example. Reviewing the job ad is key and using exact terms is essential.
Companies have their own perspective on customizing their ATS, and recruiters set up the ATS for each open role accordingly. I’ve read articles about an ATS rejecting every applicant. I’ve had clients who reach out after being rejected for a role for which they felt ideally suited, and the recruiter agreed and set up an interview.
Don’t take rejections as absolutes. It may be a “rogue” ATS, or one that wasn’t configured to parse candidate resumes properly. Always follow up. You never know!