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.
Senior embedded C developer here in the US. I can speak first hand experience at people applying to be on my team that have reasonable sounding experience and then collapse under interview questions.
Everything else you said applies here too, legally we don’t have repercussions for firing someone quickly (once had a team member for two months), but a healthy org will try very hard to get hiring right because it can cause pretty bad morale to see a revolving door and there is a massive brain and resource drain having to constantly be training new people.