Agreed, while paying to reduce spam may work in other contexts, in this setting the incentives don't align. Imagine if Linkedin got paid every time you applied for a listing, the pile of ghost jobs would be practically infinite.
Some of the listing services actually do charge employers per applicant, unless they are rejected within a certain amount of time (usually 48 or 72 hrs).
The critical distinction here is that the employer pays, not the applicant. This direction works, that's roughly how all job boards work if you squint, but if it was the applicant paying, the incentives would be opposing.
