Record the reasons for rejecting candidates - either from the company's side or from the candidate's side. This will then allow you to evaluate the reasons for which candidates most often reject you, or you can re-approach rejected candidates with a certain "good reason".
View the link for managing refusal reasons.
At the beginning, it is better to have fewer reasons so that their frequency has a telling power. If a reason has a large share, it is a good idea to analyze it and possibly break it down into more sub-reasons so that you can continuously improve your process.
You can also use refusal reasons to filter within the candidate database to create talent pools for future job outreach.