I have no idea. I don't know if it's even measurable. One could imagine calculating the number of applications by country of origin; that would give a percentage of people who did not manage to apply.
On the other hand, there are other repercussions. People don't give up. They work very hard. I've been surprised by the number of people from Africa who have been ripped off and contacted me. In that context, they may no longer have the money to submit a legitimate application.
Unfortunately, I can't give you a better answer. I can't measure what you're talking about. I haven't done the work.