So you're saying they intend to call these applicants for future roles?

Why not just post the role in the future when its ready and get applicants that way?

Read the Wikipedia article for a start.

https://en.wikipedia.org/wiki/Ghost_job

I think you have an erroneous model of how the job "market" works. Right now employers have the upper hand with tech jobs, at least junior and mid-level jobs. With so many people laid off and coming out of school competition will get most fierce at the low end. Employers don't have to care, they will get piles of applicants regardless, and can pretend to hire with online postings until it suits them to hire.

The people asking about these practices, and getting upset and indignant, either never had to search for a job before, or got their last job back when demand meant anyone who could credibly put "React" on their CV got ten offers right away. Those days have gone.