Not only does this disincentivize HR from running fake vacancies or stringing multiple candidates on just to keep their options open, but it also solves the problem of unemployed people job-searching effectively working full-time for free. The fact that companies would have to pay to hire workers would mean they try to make the selection as short and effective as possible.

Edit: From the business POV:

• Businesses would have a limited budget for hiring so would limit process to 10 applicants and would have to pick those randomly. Less time spent on interviewing but also might miss the ideal candidate. Although the difference would fall sharply with larger pools.
• And 000s of people now stuck wo any appls at all (although better than writing fake, futile appls), and no money. Not enough jobs on the market would translate into not enough paying applications for them to be able to substitute unemployment benefits.