Unlikely companies do anything with the applicants they get for these jobs other than log them in a database. Of the many reasons companies post jobs they don't intend to fill, careful A/B testing seems one of the least plausible. No place I ever worked did this to determine lowest possible salary, nor did they worry about getting too few applicants unless the number approached zero.

More likely reasons:

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

https://www.bbc.com/worklife/article/20240315-ghost-jobs-dig...